I have been going in circles on the phone with BA and AY this morning and wanted to sanity check before I go further...

I booked an AY redemption seat on AY metal via BA website using Avios. This fare includes free seat selection. My flight was cancelled and I was auto rebooked onto an earlier flight which didn't work with my schedule. I called BA to rebook onto the next morning's flight which they promptly did. It seems they rebooked me into a revenue light business fare which does not include seat selection. AY is now asking €49 for seat selection.

BA insist they cannot allocate seats on OW partner airlines and to call AY. AY says it's BA marketed so to call them but either way its a light business ticket which does not include seat selection (even after explaining the issue).

What's the best way to proceed here? The seat selection is important to me and it's why I booked using Avios in the first place. My current thinking is to pay the seat fee and claim it back from BA after the flight under UK261 since I'm entitled to comparable transport conditions (which this is not). Is this likely to work?

Any pointers would be greatly appreciated!