The real issue is they collected a specific fee from you -- $8 YYZ transit -- and you made a change so you would not be transiting through YYZ. Thus neither YYZ nor AC should get or keep the $8 (nor the feds their 40¢) and it should have immediately been credited back to you. Or else held in reserve and deducted from the fee paid the next time you did fly to or through YYZ.

I could accept AC's argument if it was the actual ticket price change that was under $10, though this should also be applied similarly to the buyer if the ticket price goes up for less than $10.

Now, if this happens on 100,000 ticket transactions a year, AC's just pocketed a cool million bucks!