Hi there - just happend the same to me today. My flight is scheduled to take off in 12 days from now. Got 100% the same mail + SMS from Air Asia. Either I pay or they will cancel after 48 hours. Booked my flights 2 months ago. Just checked that the Business Class - which I have booked - is "sold out". Maybe there is a trigger that shows if a flight is sold well, they will select those who have bought early and paid less + used their points are "selected" to get the points back and have to pay additional money.
Have you got any feedback from AA?