Those baying for GA's blood, bear in mind it's likely a case like this will be dismissed as an oddity of a niche technical nature. I wouldn't expect any staff to be briefed or compensation to be offered.
To get compensation you'll have to communicate with them in a language that they understand. If they can get away with telling you to foxtrot oscar (in more polite terms), they probably will.
Well done to MikeWh and others for their work in doing the quality technical research GA should have done. The TOCs are well aware that there are technical ticketing experts they can call on for a balanced view - but don't always like doing this before pursuing cases. If this service is outsourced to the customer then the customer should notify them it's a chargeable service at the earliest opportunity and invoice them for it. It's a scarce skill with a value and if the TOC chooses not to source it themselves and pursue the case then charge the fee once it's dropped and chase up though the County Court if needs be.
All that said however, it beats me as to why someone would want to use an Oyster card with someone else's name and photo on it. Many things that are allowed are still likely to cause problems and by the sounds of it the OP didn't know where to find the information that permitted it. If doing things like this, it's advisable to know which document allows it as clearly that would have been enough to fend off Greater Anglia.