CheckBox inside GridView getting unchecked when Button is clicked in ASP.Net

Hello,

i made a checkbox templatefield in gridview that let me select the rows wanted ...and i have a button to do something for all rows selected ...my problem is after click button i want unchech all checkbox in gridview ...i wrote this code but not working:

protected void btnPaye_Click(object sender, EventArgs e)
       {
           //TextBox1.Text = "";
         
          
           foreach (GridViewRow gvr in gdfacture.Rows)
           {
               if (gvr.RowType == DataControlRowType.DataRow)
               {
                   CheckBox cb = (CheckBox)(gvr.FindControl("chkSelect"));
                    decimal taux= Convert.ToDecimal(txttaux.Text);
                    decimal Prix= Convert.ToDecimal(gvr.Cells[1].Text) ;
                    decimal RestPaye= ((100 - taux)*Prix)/100 ;
                    DateTime DatePaiment = Convert.ToDateTime(txtdatepaiment.Text);
                   if (cb.Checked == true)
                   {
                       string constr = ConfigurationManager.ConnectionStrings["ConnString"].ConnectionString;
                       SqlConnection con = new SqlConnection(constr);
                       con.Open();
                       SqlCommand cmd = new SqlCommand("UPDATE Facture SET EtatFacture=@strEtatFacture,Taux=@strTaux " +
                           ",RestePaye=@strRestePaye,DatePaiment=@strDatePaiment,NumCheque=@strNumCheque WHERE [IdFacture]='" + Convert.ToInt32(gvr.Cells[0].Text) + "'", con);
                       cmd.Parameters.AddWithValue("@strEtatFacture", "Payé");
                       cmd.Parameters.AddWithValue("@strTaux",taux );
                       cmd.Parameters.AddWithValue("@strRestePaye",RestPaye);
                       cmd.Parameters.AddWithValue("@strDatePaiment", DatePaiment);
                       cmd.Parameters.AddWithValue("@strNumCheque", txtcheque.Text);
                       cmd.ExecuteNonQuery();
                       con.Close();
                       LabelRes.Text = "<b> Paiment </b> avec succès.";
                        
                       //cb.Checked = false; // uncheck checkBox
                        
                   }
                
               }
           }
            
           //empty the fields after insertion 
           txtdatepaiment.Text = string.Empty;
           txtcheque.Text = string.Empty;
           txttaux.Text = string.Empty;
           foreach (GridViewRow gvrow in gdfacture.Rows)
           {
               
               CheckBox chk = (CheckBox)(gvrow.FindControl("chkSelect"));
               
               if (chk.Checked)
               {
                   chk.Checked = false;
 
               }
           }
 
           //int RowsCount = gdfacture.Rows.Count;
 
           //for (int i = 0; i < RowsCount; i++)
           //{
           //    CheckBox chkDelete = gdfacture.Rows[i].FindControl("chkSelect") as CheckBox;
 
           //    if (chkDelete.Checked == true)
           //    {
           //        chkDelete.Checked = false;
           //    }
           //}
           
           gdfacture.DataBind();
           btnPaye.Enabled = false;
       }