You might be better off to contact accounting directly explaining the charge / Authorization situation. I don't have enough info to understand exactly what happened but normally a charge is only broken down if two or more tickets are purchased and the same auth is applied to all purchases. If the problem has originated at AC they can trace. If the problem resides at the bank end (two charges adding up the total charge auth but they don't see it that way) I don't have a suggestion there.
Go to this link:
http://www.aircanada.com/en/customer...etreceipt.html
Fill in the top (include ticket number)
Fill in area dealing with an explanation of what happened.
If the Card company didn't clear the original auth - they had to issue new ones for each charge - please send those so if AC has to call the card involved they will have the info to match up what happened.
Sorry to hear this happened.