Clearly they can offer an alternative, even if it means refunding the cancelled return and booking a single from MNL to the UK. So there are options via DOH even if may mean separate tickets in the first instance. Then keep an eye to see if better options appear later on. Once back in the UK you can see if you want to get advice on whether to pursue BA or JAL for either breach of contract or unfair trading - though these are non trivial areas.

I can also see things like MNL - VIE or CPH, assuming this is OK visa wise.

I wouldn't hold your breath on the complaint side - this is post travel only and is likely to be a load of unhelpful waffle.