export grid to excel display rar text

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C#

ASP.NET

i want to export grid to excel and sometimes its result(usually for one or two rows) like below


excel file:
ردی٠واحد نوع اشتراک شماره اشتراک وضعيت
1 معاونت درمان گاز 456789 فعال

and sometimes it shows correct
grid data:
ردیف واحد نوع اشتراک شماره اشتراک وضعيت
معاونت درمان گاز 456789 فعال


Code:

response.Clear();
       response.Buffer = true;
       response.AddHeader("content-disposition", "attachment;filename=ShowData.xls");
       response.ContentType = "application/ms-excel";
       //response.ContentEncoding = System.Text.Encoding.Default;
       response.Charset = "";
       StringWriter sw = new StringWriter();
       HtmlTextWriter hw = new HtmlTextWriter(sw);

       grd.AllowPaging = false;
       if (data != null)
       {
           grd.DataSource = data;
           grd.DataBind();

       }
       foreach (int Index in GridIndexLst)
       {
           grd.Columns[Index].Visible = false;

       }
       grd.RenderControl(hw);
       //string style = @"<style> .textmode { mso-number-format:\@; } </style>";
       //response.Write(style);
       response.Output.Write(sw.ToString());
       response.Flush();
       response.End();