Okay, we're on a wireless connection. I can access the marketplace, download demos and everything just fine.

But when I try to redeem a code for a Gold Subscription I get this error. I've retried a lot, and it still doesn't work. We also tried it with a different account, this time it didn't give me this error. But it said that it needed more information and prompted me to type in some info. But before I could, I got another error and it wasn't even in English, it was a bunch of boxes, and then what looked like some Japanese characters at the end.

And calling Support is getting us nowhere as the call just isn't going through.

maybe the card number is just faulty

Try to redeem it here: https://live.xbox.com/en-US/accounts/RedeemToken.aspx.

If that doesn't work then you probably have a bad card.