Error 12 when trying to submit card

I’ve issued a support ticket about this but haven’t heard back. We keep getting an error code 12 when trying to pay for our next year of hosting. We’ve triple checked the account number, expiration, CVV code and address. Everything appears to be in order.

We don’t want an interruption in service, but are having challenges giving you the money due to you. Please advise.

Error code 12 from our billing provider indicates that the payment was “declined”. Please contact your card issuer for details, using the telephone number printed on your card.

There are a couple of possible causes, but neither I nor our Support department can determine what happened — the error code is literally the only piece of information we get when this happens.