I have tried to look this up, but have not found anything on either FT or from AC itself.

I had booked a flight YUL-SJO return for spring break next year, flying PY paid in cash. While we were travelling this summer, they changed the aircraft from a 787 to an a220-330. I got the email notification from AC and the error message in the app, but I figured I would deal with it when I got home. By the time we got home, it seemed like AC had auto-confirmed it? I definitely never accepted the change, but it now just shows up as usual in the app (other than the fact that it still says premium economy and won't let me change the seat selection they gave me).

I'm not sure what I'm doing yet, but I will probably be booking in J or using our companion fare if staying in Y. I tried to cancel the booking, but because it is showing as a confirmed booking, and was booked PY lowest, it's charging me to cancel.

Is that correct, or is the fact that I am no longer flying in the fare that I booked a cause to get a full refund?

Thanks.