This might be better posted in the AA forum because it's their ticket, and they are responsible to you for your travel contract. Obviously it will be Qatar providing the service on the day.
My random guess is that Qatar might have been cranking the handle on the schedule and the flight you were originally booked on was cancelled and subsequently reinstated, but AA saw the cancellation and randomly assigned you a new flight. And although the flight might now be showing it probably has no partner award seats available on it.
You have to deal with AA to get to the bottom of what has gone on as you can't speak to Qatar in this situation. If AA are not giving you sensible answers you should specifically ask AA to reach out to Qatar via the OneWorld liaison desk to try and get the best resolution possible (ie. Partner award seats on the flight you want).
Good luck.