You say you spent £82 pre purchasing your seat, there is no seat charge of that amount on BA so the story starts to sound like sour grapes.. The seat may have been in a bad state but was still serviceable so.. Other than some avios thrown at you that is all you were entitled too, although I wouldn't except 5000 avios ( I got 15000 just for a broken TV ) so I would want at least 20000.