I'm currently in Montreal returning to YYZ on Sept.13 on AC 425 at 7pm. I was originally booked on the flight out at noon but due to some meeting changes I called my TA to change me to a later flight. She said she would do a straight exchange and there would be no charge unless AC came back and debited her. This was several weeks ago keep in mind. When I went to check-in this evening, it told me I was unable to check-in at this time. So I called AC and they tell me the exchange was never done and they want $400 in fare difference because it's no longer a 21 day advance booking. They tell me I have a confirmed seat but may be charged the difference when I check-in. AC said they could exchange the ticket but would charge me the $50 change fee plus the fare difference. Seeing as it's 12 am EST currently I am not able to get through to my TA. Any words of wisdom? I am booked into an L fare on a T+ ticket. I have emailed my TA and left a voicemail for her to call me first thing in the morning.