I have multiple account and used same credit card for the payment but last time i got a message that you have already applied this coupon ($.99) when i tried to make payment with the same credit card. Name was different, Phone Number, address everything was different only card was same.
i think they are now catching people who use different accounts to buy domains at cheaper rate.
My Suggestion: Use different card to buy domain at coupon price.
However my all accounts are safe.