How do I get a page to refresh after a SQL update to a gridview?

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SQL

C#3.5

I have a web app (C#) which has a drop down list where users choose the week ending date for timesheets:-

protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
 {
     Session["ChosenWeekEnding"] = DropDownList1.SelectedValue;
     RefreshTransactions(DropDownList1.SelectedValue);
     Response.Redirect(Request.RawUrl, true);
 }

RefreshTransactions executes the SQL query:-

protected void RefreshTransactions(string WE)
    {
        string WorkbenchConnection = ConfigurationManager.ConnectionStrings["WorkbenchConnectionString"].ConnectionString;
        SqlConnection con = new SqlConnection(WorkbenchConnection);
        con.Open();
        string sqltext = "Select JobCode, ActivityCode, WorkCentreCode, TranDate FROM JobTransactions WHERE JobTranReference = '" + WE + "' AND PersonID = 3434 ";
        SqlCommand cmd = new SqlCommand(sqltext,con);
        SqlDataReader rdr = cmd.ExecuteReader();
        GridView1.DataSource = rdr;
        GridView1.DataBind();
        GridView1.Visible = true;
        con.Close();
    }

The first time the page loads the results are valid. However using the DropDownList to change the value of WE appears to do nothing; the page remains unchanged.
I'm new to web apps using SQL, what am I missing?

What I have tried:

I've moved the Response.Redirect into various other places in the code. I've searched extensively for examples to follow; in fact what I have done was from an example.