JMich: Usual case with american banks is that they automatically decline any overseas charges, and GOG's payment passes through Cyprus (may have changed it recently, unsure about it). Check if your card can be used for international purchases, since that is the usual suspect.
paperplasticbag: Yeah I talked to them about that, They said all transactions to europe arent blocked at all. Same with gog.com
Check for blocks to Cyprus itself. Gog does their banking there. That was the holdup for me.
In the old days before I got my credit card, I would put money in my PayPal account and then pay with that to get gog games.
I do wish gig would just fix their payment issues, though. All the workarounds to everything was fine when gig was an infant. But now it's all grown up, it needs to fix these things.