Write to BA and tell them what you think of the cr@p service you recieved. Being bumped in First is nothing but cr@p.
I am absolutely astonished considering how few seats there are in First, and how much the tickets cost that BA would dream of overbooking.
Just make sure BA are absolutely clear on your views of their cr@p service.
Sounds like you've been pretty polite about all this, I'm not sure I would.