I *think* you should have gotten that seat as you were ticketed in a lower cabin than for which you had paid. This same thing happened to me once and I showed as first on the standby list and got the last F seat despite a long list of upgraders. It all depends on how the agent coded you. If I recall, the code on my BP said Z (this was 2016 before the domestic fare code changes), so I don't know if the GA got Z opened and put me in the seat or if the system was smart enough to know.
Also, FYI, there is no waitlisting awards on AA, so you were never going to clear prior to flying without calling in when there was availability.