Why ontextchanged event of textbox isnot working after postback

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C#

ASP.NET

TextBoxBase

Why ontextchanged event of textbox isnot working after postback

<div class="col-md-6">

                                <asp:TextBox ID="txtname" runat="server" class="form-control"
                            meta:resourcekey="txtnameResource1" AutoPostBack="True" ontextchanged="txtname_changed"></asp:TextBox>
                        <asp:RequiredFieldValidator ID="ReqName" runat="server"
                    ControlToValidate="txtname" Display="Dynamic"
                    ErrorMessage="Please Enter Name"
                            meta:resourcekey="RequiredFieldValidator3Resource1"></asp:RequiredFieldValidator>
                    </div>

protected void txtname_changed(object sender, EventArgs e)
       {
           int Count = m.bussinesCollection.SubscriptionKindBL.GetSubscriptionkindbyname(txtname.Text.ToString());

           if (Count != 0)
           {
               lblmessage.Visible = true;
               lblmessage.Text = "User Name is Already Exist";

           }
           else
           {
               lblmessage.Visible = false;
               m.bussinesCollection.SubscriptionKindBL.Name = txtname.Text;

           }
       }

my code works fine but during debugging i found that,when i change value in textbox if it is repatly come then that vaLUE CAN'T CHANGE.

and i can't enter new value without page refresh.

Ex. suppose i enter Asp.net in this textbox,if asp.net is already enter means it is exist in database,then labelmsg is shown.but when i try to change this value i found that if i enter any value like abcd then textbox's value become Asp.net repeatly till i not page refresh.

can anyone give me solution for that.?

Thanks in advance.