I have ordered from them before without problems and they normally reply to emails in a day or two. I am not sure, but I think the dudes name is Mike and you can send email to Mike@ whatever their email is (could be Matt but I think it was Mike... PM me if mike does not work and I will try to find the emails, has been couple months since i ordered from there)
Also, as has already been said, their should still be a number on the back of your card even if it is prepaid and they should be able to stop payment and refill your card.
JB