I use the ExcelPackage a little differently (assuming we are talking about the same DLL):
public static FileInfo existingFile =
new FileInfo(@"C:\Users\cle1394\Desktop\ExampleExcelFile.xlsx");
using (ExcelPackage xlPackage = new ExcelPackage(existingFile))
{
ExcelWorksheet worksheet = xlPackage.Workbook.Worksheets[1];
// clear value
worksheet.Cell(iRow, 1).Value = "";
}
Try that, let me know if it works.