Look for extra spaces in your values' cells. If your duplicate values have extra spaces in their cells, those spaces will also cause the Remove Duplicates tool to consider them to be unique values.

How to Remove Extra Unused Cells in Microsoft Excel 2013. Worksheets in Microsoft Excel can contain over a million rows and over 15,000 columns. With a workspace that large, if you're not careful ...

You can remove leading, trailing, and extra spaces between characters and numbers in Excel using TRIM (), SUBSTITUTE () or Find and Replace.