ถามหน่อยครับ import excel ไฟล์ .xlsx ได้แต่ไม่สามารถ import ไฟล์ .xls ได้ครับ ต้องแก้ยังไงครับ

           try
            {
                int x = 1;
                FileInfo excel = new FileInfo((@"D:\Application\Billpayment\FileTest\COOP_180531_012.xls"));
                using (var package = new ExcelPackage(excel))
                {
                    var workbook = package.Workbook;

                    //*** Sheet 1
                    var worksheet = workbook.Worksheets.First();

                    string strConnString = "Server=xxxxxxxxxx;UID=sa;PASSWORD=xxxxxx;database=mybase";
                    var objConn = new SqlConnection(strConnString);
                    objConn.Open();

                    //*** Loop to Insert
                    int totalRows = worksheet.Dimension.End.Row;
                    for (int i = 10; i <= totalRows; i++)
                    {
                        MessageBox.Show(worksheet.Cells[i, 1].ToString());
                        string strSQL = "INSERT INTO tbl_billpayment_confirm (billpayment_date,order_no,ref_no_1,ref_no_2,billpayment_name,amount,status_flag,user_id) "
                            + " VALUES  ("
                            + "GETDATE()" + ", "
                            + " '" + x + "', "
                            + " '" + worksheet.Cells[i, 1].Text.ToString() + "', "
                            + " '" + worksheet.Cells[i, 2].Text.ToString() + "', "
                            + " '" + worksheet.Cells[i, 3].Text.ToString() + "', "
                            + " '" + worksheet.Cells[i, 4].Text.ToString() + "', "
                            + " '" + null + "', "
                            + " '" + null + "' "
                            + ")";
                        var objCmd = new SqlCommand(strSQL, objConn);
                        objCmd.ExecuteNonQuery();
                        
                    }

                    //objConn.Close();
                    MessageBox.Show("เสร็จ");
                    x++;
                }
            }
            catch (Exception ex)
            {
               MessageBox.Show(ex.Message);
            }
        }