Check with the operating carrier if the booking has come through.

I had a similar problem but with opposite roles. QF did the change and AA operated the flight. Booking did not exist for AA and I had to fly ORD-BOS via YYZ instead of nonstop because all direct services were full. I also lost all susequent legs because of "no show" (AA claimed QF made a double booking instead of a date change). Nevertheless QF claimed everything was fine in their system - thus better check with the operating carrier (if they say you're booked, then you're fine, no matter what the booking carrier says).

BTW, do AA and QF have problems in booking each other's flights? Does anybody know more about this?