Outstanding...

[Focault]

It isn't a scam. The OP paid for some time frame with a credit card that was then charged back and/or renounced by the supporting bank. This pulled the funds back out of Blizzard's bank account. They want to be paid for that in a secure method (money order) first before the OP will be able to set up payment method going forward. Once they are evened up he'll be able to use a credit card (not the same one I'm sure though) on the account again.

His phone call to them should clear it all up.

[Deleted]

Then why do they accept credit cards =/

good question and one I can answer.
a credit card's credit is essentially a loan, complete with a payment plan and interest and all those silly things.
when you use a credit card's credit (instead of the debit) you take a loan with whoever gave you the credit card, and you use this loan in this case to pay blizzard. blizzard gets the money they wanted and are happy, and you are stuck with a loan to whoever gave you your credit card.