Wanted to post an update on my situation and ask for some advise. Long story short, my flight from LHR to IAH in business that I purchased with AA miles was cancelled and I was rerouted via PHL in economy. The LHR to PHL flight was delayed due to a flight attendant being sick and I missed my PHL to IAH flight for which I was placed on a flight for the next day. I requested 3 compensations: 2 for delayed flights (LHR-IAH and LHR-PHL-IAH) and 1 for the downgrade.

So far BA has given my 520GBP for the LHR-IAH cancellation. Via email I had a back and forth with BA about compensation for the rerouted LHR-PHL-IAH which was also delayed and they claimed only the initial flight was applicable for this compensation and they pointed me to AA for the downgrade compensation. Thanks to AviosTreasureHunter for letting me know about the double compensation.

I filed 2 separate CEDR complaints, one for the LHR-PHL-IAH delay and one for the downgrade. For the flight delay, BA argued that I already had a complaint open for this flight (for the downgrade) and based on CEDR rules I was only allowed to open one for a given flight. CEDR agreed. I explained the situation and CEDR understood. They eventually combined my 2 complaints into 1.

Today BA has finally responded to the complaint and offered my 520GBP per passenger but again point me to AA for the downgrade refund. Everything that I have read says that BA are still responsible for the 75% refund even though it was purchased with AA miles. Now that the complaints are combined I don't want to risk losing the 520GBP but the downgrade compensation comes out to 1200GBP for the miles and taxes. How should I respond to this offer?