This sounds like a great injustice. Although, I agree that
there can be no substitute for the real thing (a 2012),
the dealership should be trying to do their best at making
things right for you the best that they can.
You trusted that GM dealership with something valuable to you,
and they broke that trust, that is very bad business practice.
It sounds like there is not a C5 member here who will not
stand behind you on this one.