I need some help from some compensation experts please. So much disruption and so many airlines, I don't even know who I'm claiming compensation off.

Original booking DUB-HEL-HKG with second leg in Premium Economy. First sector cancelled due strike action, rebooked DUB-LHR-HKG, British Airways onto Cathay and second leg still PE.

BA very late, missed the LHR-HKG flight. Rebooked onto the next but now downgraded due no space in PE. Cathay say BAs problem but will BA say ticket was simply endorsed over from AY and nothing to refund?

Some help on where to direct my now mounting compensation requests would be appreciated (already have being moved to a flight three hours earlier!). Does it all just go to AY and they sort it out in the backend?

Many thanks!