I had the same problem with a flight last week. Called the AAdvantage Desk and the agent argued with me for 10 minutes that 'C' was my original booking class and that I couldn't possibly have booked 'P' because 'P' is a paid business class fare. 😒 She finally at least partially understood and changed the EQM credit to 'Y'. How is it possible that that the AAdvantage agents still don't know what premium economy is?