Something similar happened to me with Blizzard. I'd buy subscription time and, a few days later, they'd cancel my subscription and refund the charge. After a few rounds of this, they suspended my account.

In that case, I appealed and was told, for the first time, that the reason for the refunds was that the card I'd been paying with didn't match the stored payment information saved to my account.

Both cards were equally valid and there was no indication anywhere that having saved payment information disqualified you from paying by any other method. As best I can tell, Blizzard just updated their policies one day for no particular reason, then made not complying with the new, secret policies a bannable offense.