Single, with a return on a 2nd ticket.
The single was £144 advance first class
That's a shame.
It's a ridiculous situation that you are in, having erroneously been charged. In your shoes I'd have refused to pay based on the fact that I had received permission to travel with the information that I had and thus was not in breach of the bylaw, but that's just me.
Your only real options are customer services, transport focus, then progress to the media