Seat allocation after re-routing. (BA Silver on Malaysian).

I purchased a cash ticket from LGW to HKT from the BA website. Flight at the end of April. This was to be operated by Qatar and therefore stopping in Doha. Not surprisingly, this was cancelled.

I was offered a re-route on Malaysian via KL. Not ideal, but this is OK.

With Silver, I should normally select seats at the time of booking, as I did with the original Qatar booking but this is not possible on the Malaysian App/ Website without paying.

The Malaysian App/Website says I can select seats free of charge, however the actual process wants payment if I try to proceed.

Does anyone know:

• Should I get seat selection from booking as if it were a BA flight?
• Is this included in 261?
• Is this something specific with Malaysian bookings where they don't honour BA status, or is it likely to be a glitch because of the re-routing.

I have spoken to BA and Malaysian who both tell me it's the responsibility of the other.

The BA App and Website tell me seat selection is unavailable.

My BA frequent flyer number is appearing on the Malaysian app/website when I enter the booking details.

I was silver at the time of booking and will remain silver for the coming year.

Can anyone tell me what I should be entitled to?