The exact same thing happened to me with Gamecarddelivery. I bought two PSN cards, neither were working. I called up Sony and it turns out both cards were redeemed a month earlier. They sold me used cards basically. I contacted them, and they asked for proof that I did not use those cards. Interestingly, no matter how much proof I provided (I even contacted Sony and got them to send me an email confirming the cards were used prior to my purchase), they continued asking for more proof. After a while it seemed pointless to continue trying to resolve this with them. Then I tried to get help from PayPal, and of course they did nothing because apparently prepaid cards are not covered under purchase protection.
I know it's a little bit off topic, but since this is the thread that pops up when you search for gamecarddelivry on google, I thought this is the best place to warn people.