Originally Posted by
metaxo
I contacted AC customer support. They told me first that "The flight had been cancelled by United Airlines you will need to contact United Air for rebooking assistance."
Surely United cannot cancel an air Canada flight. Maybe they cancelled the OP's reservation? Although as the OP says AC781 seems no longer to exist, so it likely is the case that Air Canada cancelled 781 and rebooked on 783. Which incidentally seems to full in business.
I asked more, and they then replied "the ticket is still valid, but "make sure that everything is properly confirmed with United Airlines, due to the fact that we only had a slight schedule change for which you were notified about". Another employee confirmed on the phone that the ticket is still valid.
"Ticket is still valid" is unclear, might mean that it still includes that leg, or that the ticket is still there but that leg might have been removed. In other words, that there no longer is a reservation attached to it for that leg.
What does aircanada.com show for that reservation/ticket?