I do feel for you in this situation, however sadly outside of A3, this is how a lot of airlines in Europe are from this POV. And I find Southern European countries, every thing is just done by the book (if you are a nobody) and this is most probably what happened. I am sure it would have been the price being quoted for any walk up passenger that day for that same flight which. They seem to prefer to let the seat go out empty instead letting one fly in that seat without the asking price.
I too have been caught in so many similar situation - which I can never understand how RM operates and in the big picture how airlines in these situations work - compared to airlines in the US where these situations are handled much better compared to here in Europe/Asia.

Cheers!