public void CombinarCeldas(string celdaInicial, string celdaFinFinal)
        {
            MergeCells mergeCells;

            if (_workSheet.Elements <MergeCells>().Count() > 0)
            {
                mergeCells = _workSheet.Elements <MergeCells>().First();
            }
            else
            {
                mergeCells = new MergeCells();

                if (_workSheet.Elements <CustomSheetView>().Count() > 0)
                {
                    _workSheet.InsertAfter(mergeCells, _workSheet.Elements <CustomSheetView>().First());
                }
                else
                {
                    _workSheet.InsertAfter(mergeCells, _workSheet.Elements <SheetData>().First());
                }
            }
            MergeCell mergeCell = new MergeCell()
            {
                Reference = new StringValue(celdaInicial + ":" + celdaFinFinal)
            };

            mergeCells.Append(mergeCell);
        }