Import Excel Sheet to Database using C#

if (Path.GetExtension(FileUpload1.FileName) == ".xls" || Path.GetExtension(FileUpload1.FileName) == ".xlsx" && (FileUpload1.PostedFile.ContentType == "application/vnd.ms-excel" || FileUpload1.PostedFile.ContentType == "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet"))
{
    string uploadedFilePath = Server.MapPath("~/docs/" + System.IO.Path.GetFileName(FileUpload1.FileName));
    FileUpload1.SaveAs(uploadedFilePath);
    postedfile = uploadedFilePath;
    switch (postedfile.Substring(postedfile.LastIndexOf('.') + 1))
    {
        case "xls":
            stringConExcelMat = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" + uploadedFilePath + ";Extended Properties=\"Excel 8.0;HDR=NO;IMEX=1\"";
            break;
        case "xlsx":
            stringConExcelMat = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" + uploadedFilePath + ";Extended Properties=\"Excel 12.0;HDR=No;IMEX=2\"";
            break;
    }
}
else
{
    ScriptManager.RegisterStartupScript(this, this.GetType(), "fdfd", "alert('Only (XLS,XLSX) Extension Files are allowed.Or Content-Type Mismatched');", true);
    return;
}
DataTable TTable = new DataTable(postedfile);
using(OleDbConnection conn = new OleDbConnection(stringConExcelMat))
{
    conn.Open();
    using(OleDbDataAdapter da = new OleDbDataAdapter("SELECT * FROM [Sheet1$A:T]", conn))
    {
        da.Fill(TTable);
        if (TTable.Rows.Count > 0)
        {
            string sqlConnectionString = System.Configuration.ConfigurationManager.AppSettings["strConn"].ToString();
            using(SqlBulkCopy bulkCopy = new SqlBulkCopy(sqlConnectionString))
            {
                bulkCopy.DestinationTableName = "Upcoming_SaleList";
                bulkCopy.WriteToServer(TTable);
            }
        }
    }
}