We're going to need a lot more information to be able to give a useful response.

Does this still happen to your relative when they try to go to aa.com? Do they have any screenshots? What was the phone number? Probably even more than that, but based on your description of the problem it seems very unlikely aa.com was hacked. If the hackers could do that, they could just get your relative to type their credit card into the hacked site and steal the number that way.