I have a question I'm hoping someone can give me a steer on:

Through BA Holidays, I booked EDI-LHR-HKG return with hotel, and a 1 night stopover at LHR outbound.

I paid for Clubworld return and used 30,000 Avios to upgrade to First Outbound.
On 31st May, in the Concorde Room, I received a call to advise that due to an aircraft change, I was unfortunately being downgrade as the replacement aircraft had no First Cabin (changed from 777-300 to 777-200).

Impressively, the lady came to see me in the CCR and handed me £500 compensation Prepaid Mastercard and opened a CR case for refund of 75% of sector affected.

My question is: as the booking was BAH, and I have no sight of the flight/hotel breakdown, is there a way of establishing the flight cost, and therefore what refund I could expect? Does the Avios-For-Upgrade factor change the possible refund value?

(I should add, I was told the reason for the aircraft change was due to out-of-position aircraft as a result in the bank holiday weekend issues. I assume that this doesn't fall into "exceptional circumstances" that could prevent the claim, especially when BA themselves opened the case and have already paid the compensation element?)

Any advice is appreciated