not exiting the task manager after closing also

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hi i declared code to display the excel to export after exporting the code i am exit the application even also the memory leak in the task manager it is not at closing excel file which is exporting by this im facing the problem in two ways
one is not allowing to open file to other files some times it is facing
another is eating the lot of memory
in this i am addiontaly declared the code is

public void SetCellValueToTextOnActiveSheet(int row, int col, object val)
         {
             //Rng.NumberFormat = "Text";
             Rng.NumberFormat = "###0";
             Rng.Value2 = Convert.ToString(val);
         }

which is for to convet the excel file number which are big will not display as it is so i convertd into it as text
and in the main class i declared it as

if (Dt.Columns[j].ColumnName == "Serial In" || Dt.Columns[j].ColumnName == "Serial Out")
                            {
                                Xl.SetCellValueToTextOnActiveSheet(2 + i, 1 + j, Row[j].ToString());
                            }
                            else
                            {
                                Xl.SetCellValueOnActiveSheet(2 + i, 1 + j, Row[j].ToString());
                            }
                        }