Unable to purchase ZP anymore.

I have been buying ZP on and off for a while now, mainly with prepaid credit cards. All of the sudden one day It gave me this message after clicking on the amount I wanted to purchase

"This transaction has been denied.
Reason:Failed to pass security validations."

I didn't even get to enter the credit card information. I double checked the card on the companies website, and it says I have enough of an available balance to be able to purchase it, but it will not let me.

I had also recently been paying with my paypal account. From there it would let me pay directly from my bank account to the game. All of the payments have come out of my account, and I received the ZP for them, but the other day I tried again and it says that the option to pay directly from my bank is all of the sudden not available, and it defaults to a credit card that was a prepaid one I had attached a while ago. I have more than enough money in the bank to cover the transaction, but all options other than pay by credit card are grayed out.
While it is saving me money that I should in face be... saving. It still troubles me that I no longer seem to have a way to purchase ZP at all. To the best of my knowledge I don't think I can get any of those prepaid cards here.