Hi, for years I‘m a silent reader here no it‘s finally my time to post something:

I booked through my company tool from MEX - YYZ - FRA on AC. The company tool is set to use my TK number for all star alliance flights but instead of TK my EY number was added to the booking. When I noticed this I tried to change from EY to TK but it was not possible online or via app. I contacted the company travel agency also they were not able to change it to TK.
Once I arrived at the checkin in MEX I asked staff to change my frequent flyer number to TK. It took her a while but she was able to change it and my boarding pass showed the TK*G

After couple of weeks I wondered why the miles were not credited yet. I claimed it with TK and they said the miles were already credited with another airline.
I found out that despite the fact that my boarding pass showed TK*G the miles still got added to my EY account.

EY will not revert it and TK will not credit it as its already with EY.

Anyone has an idea how to get the miles credited to TK? Even more annoying: These are the last miles I needed to requalify

Yeah, that’s always a problem. There are 2 fields, one is for accrual and one is for status. Your TK*G was probably added for status while the EY remained for accrual. Sounds like your TA is at fault for messing this up. In the future, the best way is to have them completely remove the FQTV - then re-add. Nothing you can do here unless you get EY to revert the credit.