Created Unassigned: SaveAs changes existing format in excel sheets [9502]

I have already excel template which has already inserted with some formulas and formats to the cells.

This excel will open using application and saves necessary changes to sheets. and save the excel using saveas method.
wb = new XLWorkbook(FileName);
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wb.CalculateMode = XLCalculateMode.Auto;
wb.SaveAs(FileName);

After saving, the excel formats are getting changed completely and calculations are going wrong. Percentage columns are changing to Date format. How can I proceed here by saving excel without changing existing formats. attached correct and incorrect excel.

Regards