I had this once with a printer I had bought from PC World - the points posted but were removed months afterwards for some reason (no returned goods).
I contacted BA and they asked for a copy of the receipt - which I still had but it had faded so much that reading the original was almost impossible, so they refused to re-add the points as the receipt copy was also of such poor quality.
So their systems seem to be a bit strange. If you have legible receipts I would think you could get them reinstated.