After 3 hours on the phone, I didn't end up booking any flights.

At the start everything was going smoothly and I was able to get everything booked, but then when she tried to put it through, she said that it was over mileage on the return. This was the itinerary.

YYZ-IAD
IAD-SFO
SFO-AKL (Stop)
AKL-ZQN (had to do connecting, no availability)
ZQN-MEL (Destination/Turnaround)
MEL-PVG (less then 24 hr connect)
PVG-NRT (Stop)
NRT-SEA
SEA-YYZ

She said that even if I cut out the PVG connecting, I still wouldn't be able to book. The only way I was going to have this work is if I had a direct back from NRT to YYZ and there was no availability. She said even if I went MEL-SIN-PVG-NRT, I would be more over the mileage so that wouldn't work. I was trying to book in Y class as well.

Does anyone know if there was something she could have done to make this work? I asked if she could do an exception cause doing the direct would be great, but I was ok with the connecting. I was thinking the connecting is more of an inconvenience compared to the direct and since there was no direct, perhaps something could be done. Unfortunately, she said that there was nothing she could cause they have to follow the rules.

Is the mileage rule for this route - YYZ-MEL multiple by 1.2 to get the total mileage for the return and I start to minus for each leg of the trip to return?

I was hoping that this could be done, but from the looks, you can't use united on the return and you have to use AC.