if else is giving weird output in transaction query

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VB

MS-Access

transaction

Below is my code for updating items in a invoice .
i add some items , and update some items based on values but it is just inserting or updating the same values to all the rows . I think the paramerters are creating the problem , please guide me to rectify the fault .

con.Open()
            tra = con.BeginTransaction
            sqlstr = "UPDATE transaction_Mas_Tab set billdate=@billdate,invoiceno=@invoiceno,TotalBillamt=@TotalBillamt,narration=@narration,orderdate=@orderdate,usercode=@usercode,lcode=@lcode,remarks=@remarks,grossamt=@grossamt where txid=@txid "
            cmd = New OleDbCommand(sqlstr, con, tra)
            cmd.Parameters.AddWithValue("@billdate", dtpbilldate.Text)
            cmd.Parameters.AddWithValue("@invoiceno", txtinvoiceno.Text)
            cmd.Parameters.AddWithValue("@TotalBillamt", Val(txtgt.Text))
            cmd.Parameters.AddWithValue("@narration", txtnote.Text)
            cmd.Parameters.AddWithValue("@orderdate", dtpbilldate.Text)
            cmd.Parameters.AddWithValue("@usercode", usercode)
            cmd.Parameters.AddWithValue("@lcode", cmbparty.SelectedValue)
            cmd.Parameters.AddWithValue("@remarks", txtrmrks.Text)
            cmd.Parameters.AddWithValue("@grossamt", Val(txttotalamt.Text))
            cmd.Parameters.AddWithValue("@txid", txid)
            cmd.ExecuteNonQuery()
 For c As Integer = 0 To dgvsitemlist.Rows.Count - 1
                If dgvsitemlist.Rows(c).Cells("onew").Value.ToString = "N" And dgvsitemlist.Rows(c).Cells("isdel").Value.ToString = "N" Then
                    sqlstr = "insert into transaction_details (txid,itemid,unit,irate,iqty,isdeleted)  values(@txid,@itemid,@unit,@irate,@iqty,@isdeleted)"
                    cmd = New OleDbCommand(sqlstr, con, tra)
                    cmd.Parameters.AddWithValue("@txid", txxid)
                    cmd.Parameters.AddWithValue("@itemid", dgvsitemlist.Rows(c).Cells("itemid").Value.ToString)
                    cmd.Parameters.AddWithValue("@unit", dgvsitemlist.Rows(c).Cells("unitid").Value.ToString)
                    cmd.Parameters.AddWithValue("@irate", Val(dgvsitemlist.Rows(c).Cells("prate").Value))
                    cmd.Parameters.AddWithValue("@iqty", Val(dgvsitemlist.Rows(c).Cells("qty").Value))
                    cmd.Parameters.AddWithValue("@isdeleted", "N")
                    cmd.ExecuteNonQuery()

                    sqlstr = "INSERT INTO IMasterDetails ( icode,batch,prate,srate,opstock,clstock,pscheme,sscheme,itemid) values (  @icode ,@batch , @prate , @srate,@opstock,@clstock,@pscheme,@sscheme,@itemid )"
                    cmd = New OleDbCommand(sqlstr, con, tra)
                    cmd.Parameters.AddWithValue("@icode", dgvsitemlist.Rows(c).Cells("icode").Value.ToString)
                    cmd.Parameters.AddWithValue("@batch", dgvsitemlist.Rows(c).Cells("batch").Value.ToString)
                    cmd.Parameters.AddWithValue("@prate", Val(dgvsitemlist.Rows(c).Cells("prate").Value))
                    cmd.Parameters.AddWithValue("@srate", Val(dgvsitemlist.Rows(c).Cells("srate").Value))
                    cmd.Parameters.AddWithValue("@opstock", Val(dgvsitemlist.Rows(c).Cells("qty").Value))
                    cmd.Parameters.AddWithValue("@clstock", Val(dgvsitemlist.Rows(c).Cells("qty").Value))
                    cmd.Parameters.AddWithValue("@pscheme", dgvsitemlist.Rows(c).Cells("pscheme").Value.ToString)
                    cmd.Parameters.AddWithValue("@sscheme", dgvsitemlist.Rows(c).Cells("sscheme").Value.ToString)
                    cmd.Parameters.AddWithValue("@itemid", dgvsitemlist.Rows(c).Cells("itemid").Value.ToString)

                ElseIf dgvsitemlist.Rows(c).Cells("onew").Value.ToString = "O" And dgvsitemlist.Rows(c).Cells("isdel").Value.ToString = "N" Then
                    sqlstr = "update transaction_details set itemid=@itemid,unit=@unit,irate=@irate,iqty=@iqty,isdeleted=@isdeleted where txid=@txid"
                    cmd = New OleDbCommand(sqlstr, con, tra)
                    cmd.Parameters.AddWithValue("@itemid", dgvsitemlist.Rows(c).Cells("itemid").Value.ToString)
                    cmd.Parameters.AddWithValue("@unit", dgvsitemlist.Rows(c).Cells("unitid").Value.ToString)
                    cmd.Parameters.AddWithValue("@irate", Val(dgvsitemlist.Rows(c).Cells("prate").Value))
                    cmd.Parameters.AddWithValue("@iqty", Val(dgvsitemlist.Rows(c).Cells("qty").Value))
                    cmd.Parameters.AddWithValue("@isdeleted", "N")
                    cmd.Parameters.AddWithValue("@txid", txxid)
                    cmd.ExecuteNonQuery()

                    sqlstr = "Update IMasterDetails set icode=@icode,batch=@batch,prate=@prate,srate=@srate,opstock=@opstock,clstock=@clstock,pscheme=@pscheme,sscheme=@sscheme where itemid=@itemid "
                    cmd = New OleDbCommand(sqlstr, con, tra)
                    cmd.Parameters.AddWithValue("@icode", dgvsitemlist.Rows(c).Cells("icode").Value.ToString)
                    cmd.Parameters.AddWithValue("@batch", dgvsitemlist.Rows(c).Cells("batch").Value.ToString)
                    cmd.Parameters.AddWithValue("@prate", Val(dgvsitemlist.Rows(c).Cells("prate").Value))
                    cmd.Parameters.AddWithValue("@srate", Val(dgvsitemlist.Rows(c).Cells("srate").Value))
                    cmd.Parameters.AddWithValue("@opstock", Val(dgvsitemlist.Rows(c).Cells("qty").Value))
                    cmd.Parameters.AddWithValue("@clstock", Val(dgvsitemlist.Rows(c).Cells("qty").Value))
                    cmd.Parameters.AddWithValue("@pscheme", dgvsitemlist.Rows(c).Cells("pscheme").Value.ToString)
                    cmd.Parameters.AddWithValue("@sscheme", dgvsitemlist.Rows(c).Cells("sscheme").Value.ToString)
                    cmd.Parameters.AddWithValue("@itemid", dgvsitemlist.Rows(c).Cells("itemid").Value.ToString)
                    cmd.ExecuteNonQuery()

                ElseIf dgvsitemlist.Rows(c).Cells("onew").Value.ToString = "O" And dgvsitemlist.Rows(c).Cells("isdel").Value.ToString = "Y" Then
                    sqlstr = "update transaction_details set itemid=@itemid,unit=@unit,irate=@irate,iqty=@iqty,isdeleted=@isdeleted where txid=@txid"
                    cmd = New OleDbCommand(sqlstr, con, tra)
                    cmd.Parameters.AddWithValue("@itemid", dgvsitemlist.Rows(c).Cells("itemid").Value.ToString)
                    cmd.Parameters.AddWithValue("@unit", dgvsitemlist.Rows(c).Cells("unitid").Value.ToString)
                    cmd.Parameters.AddWithValue("@irate", Val(dgvsitemlist.Rows(c).Cells("prate").Value))
                    cmd.Parameters.AddWithValue("@iqty", Val(dgvsitemlist.Rows(c).Cells("qty").Value))
                    cmd.Parameters.AddWithValue("@isdeleted", "Y")
                    cmd.Parameters.AddWithValue("@txid", txxid)
                    cmd.ExecuteNonQuery()
                End If

            Next

            tra.Commit()
            updatebilldata = txid
            clearall()
            clearsave()
        Catch ex As Exception
            MsgBox("Some thing Went Wrong")
            tra.Rollback()
            updatebilldata = Nothing
        End Try


    End Using