Hi bumonseat,
Welcome to Flyertalk and the BA Board...
I am very disappointed to hear of your experience. It shames me that the aircraft carry British Airways titles on them. The service you received onboard sounds truly awful, and totally unacceptable. Some of the information you were given sounds a little incorrect. Openskies, a wholly owned subsidiary of British Airways bought L'Avion, which consisted of 2 757 aircraft, which is one of the ones that you flew on. You are correct, that the onboard cabin and seats are completely different from the Openskies product and seats. I too would be highly disappointed if my food were served on plastic on a Business Class airline.
Best of luck with your complaint,
Regards,