I personally am happy to hear this. Way too many people (not saying you are) take large carry-ons and numerous bags that it has gotten ridiculous. The overhead bins end up full before everyone is even on the plane because people put them up as they walk on and not above their own seats. We have gotten to our seats and there is no room even for my CPAP machine and is very frustrating.
Our last few flights they always ask if anyone is willing to check their carry on bag for free. I think it is long overdue for them to start enforcing the carry on size.
For you personally, I’d check on the AC website and if in fact your bag is within their limits, I’d put in a complaint for a possible refund.