There have been a lot of reports of this — supposedly because the same fare class from the flight credit needs to be booked — but it's really shady that you weren't informed before the charge, which has also happened to others.

If I were you, I'd book the $577 ticket from scratch and then demand a full refund of the $949 at https://prefunds.aa.com or even via DOT complaint, if necessary. After that — definitely separately from the refund request — you could submit proof of the $470 fare you had on hold and ask for a credit or refund of the difference between $577 and $470.

A few people have had success requesting flight credits be converted to trip credits or paper vouchers, which, if granted, should avoid this problem in the future.