If you were earning AAdvantage miles, you'd take this up with AA; as you are earning Avios / Tier Points, you need to take it up with BAEC.
I have no idea how BA treats requests for original routing credit when you were involuntarily rerouted (that's the terminology we'd use with AAdvamtage), but the BAEC Forum would be the place to ask; I will forward this there now. Good luck.
JDiver
senior moderator