Delete identical ignores identicals

[LuciaWilting]

Info:

   New user (1 month)

   Use for historical GIS (History major student)

   Question/ issue:

         I have a large selection of entries, some of which are duplicates to the point where the unique identifiers (perceelnummer = parcelnumber) sometimes show up in doubles. I tried to get rid of them using the "Delete identical" tool, but as the image shows, it completely ignores two identical parcelnumbers. Using the tool on various other identical values does not work either.

Any ideas on how to make this work? 

[JakeSkinner]

Hi Lucia,

Can you upload a small sample of your data (i.e. export some features to a new feature class in a new File Geodatabase > zip the .gdb > upload the zip file)?