A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
I see you've asked the same question in the Excel for Windows Community. That may be the source of the confusion.
The Windows version offers more Underline styles than the Mac version. If the underline was applied in Excel for Windows the only suggestions I can offer are to either;
- remove the underlining then reapply it, or
- use Edit> Clear - Clear Formatting then apply Underlining