It sounds like your company reserves B, not A. In which case you definitely should complain when not given a C mid-size.

That also could be the source of confusion. As President's Circle you should always be getting a C mid-size when you are reserving B compact. Gold Choice does require you to reserve C mid-size, but there is some ambiguity in that a President's Circle compact reservation is the equivalent of any other member's mid-size reservation, by virtue of the guaranteed upgrade.

So, 9 out of 10 times, you get upgraded to a car above mid-size. It's a bit of reach then to say you can have this upgrade, but you can't have a Gold Choice equivalent upgrade.

Then the time you got the Fiesta, the person at the gate probably didn't realize you had been wrongfully (mistakenly) denied your President's Circle upgrade.

Just remember, these airports get so much business that at times they can barely keep on top of what car is where. I find that when mistakes happen, but if you grant them the benefit of the doubt, they will work hard to make things right.