Oh! All is not lost however - Send it back to me and I will make an interference fit sleeve to go inside the 16mm that is drilled out to either the 12mm or 13mm you need.
You do need to tell me the exact diameter of the tube though so I can drill out to right size.

When the face is machined / polished anew you will hardly be able to see the hairline where the two join.

Other option is I can reuse your VW on a PL-71 order I have as that needs a bit centre hole...

I think loads of elec tape will have the same effect as the Rega counterweight stub that OL replaces with proper solid one to fit CW on.