So long as you’ve acted reasonably, BA will refund this in the end. Don’t get in a protracted battle with them - if they refuse just ask for a deadlock letter/get them to confirm the £150 is their final offer - and head off to CEDR or MCOL. Either would do, I suspect - CEDR would be free but a bit slower, MCOL would cost you up-front, which you’d recover if you win, but might shave a week or two off.

BA no longer hands out Avios on a discretionary basis for service failures and the like - they’ve moved to vouchers, and I’d have to say in this case I think you’ll be lucky to get anything other than your legally entitled money back. In fact, the more complications and demands you add to this claim, the more you’re likely to muddy it and delay the outcome. You certainly don’t want to include such a request in a legal submission - it’ll damage your case rather than help it.