Cancelled flight rebooking transferred to another airline and original airline unable to do anything

Booked a family trip to Europe in Oct/Nov for the following July. Return trip was set to be from Zurich to London (on British Airways) then London to final US destination (on American Airlines). Entire trip was booked through American Airlines. The Zurich-London flight was scheduled for 7:15am local, so we went to bed early and had car service booked for 4:30am.

Woke up at 4am to find an email cancellation from 2am from British Airways for the Zurich-London flight, and an automatic rebooking on Zurich to Toronto then to final US destination, all on Air Canada. New Zurich flight was at 1:30pm local, and the whole trip would delay our final arrival in US by over 6 hours, and now we were already awake for the day (at 4am, or 10pm Eastern). We wanted some flexibility to choose an earlier flight if one existed, rather than accepting an automatic rebooking with a 6 hour delay and travel to another country on another airline, which was not part of our original plan. We found an earlier flight combo on American that would work for us and had enough seats available.

The worst part is that when we called American Airlines (who managed the original booking), to request an adjustment, they told us to call British Airways since it was their cancelled flight. Then British Airways said to call American. American then said they couldn’t do anything at all, because the flight booking was now owned by Air Canada. Apparently once Air Canada “released” the flight booking, American could get involved. Of course none of this could be done behind the scenes. Almost 2 hours on the phone across 3 airlines, at 5am, and American finally rebooked us on a flight from Zurich to Philadelphia then to final US destination (all on American).