There are - I believe - 2 paths open to you. First is to keep calling BAEC until you get a representative who is prepared to resolve the matter. The alternative, after 8 weeks from the first complaint, you complain to CEDR not for EC261 reasons but because you feel the airline has not treated you fairly. It's possible CEDR will say "we don't get involved with loyalty schemes", though I don't know whether this will happen. I guess you could also look at MCOL but the risk of that one is that in essence BA (or rather AGL) is the underlying owner of Avios and the scheme, so they have lots of discretion to act, not act, here.