I agree with RESGIRL on this. It seems that the first agent might have made an error in allowing you to use your first flight credit together with the remainder of the ticket. AFAIK flight credits cannot be combined, and in this case AC did, it makes reissuing a total headache.

FYI : There's something wrong in your fare calculation as quoted by you -

Fare Calculation: 09FEB09YYJ AC X/YVR AC YTO Q21.61R217.04AC YVR Q21.60R172.87AC X/YTO AC SIN R323.20AC X/HKG AC YTO Q4.22R811.77NUC1572.31 END ROE1.064330 XT420.00YQ23.51SGPD15.89CA1.50XG30.00SQ

Why are you flying... YYJ - x/YVR - YYZ and then back to YVR and back to YYZ, then straight to SIN. How are you getting from YYZ to SIN. Where is your NRT transit? Then from SIN - x/HKG - YYZ. Where is the end point? YYJ? From how I see it, the fare calculation is entirely wrong anyway! No wonder no one wants to touch it anymore!

If it might help you in any way, GO to the nearest airport and AC ticketing counter and sort out your ticket there and then. AC res people are not fares/ticketing people and they take all info down to be relayed to the fares department. The fares dept will have to go with what the fare rules say, and usually their account is very different.

But the airport ticketing staff are very well versed in all ticketing aspects. They will look at your case and try to see where the problem lies. So I would suggest in not wasting your time calling AC res anymore and just go to an actual ticketing desk.

Remember though what the first/2nd/3rd call centre agents said will now be irrelevant when you're talking to the ticketing agents cos they will go according to the rules of the ticket, the fare credits and the rules based on your ORIGINAL tickets.

Good luck.