Originally Posted by bisonrav

[EDIT: I revoke my certainty given the details below about the old old old card]

This is a really easy process which I think you've overthought and made difficult for yourself.

You request the refund from BA, this will go back to the original amex card account.

You chat to or call amex and explain the situation, giving the previous card details (last 5 digits). They will then ask for bank details and a few days later the refund will appear. I've done this a few times, it is always extremely easy. I've done something similar with other cards (Creation IHG) and it has been relatively straightforward but a little more involved. It happens a lot, the card companies know what to do. Step outside the normal process and you're likely to hit snags.