This is a known scam that's been around for ages. Basically it's always someone that has a self moderated thread, sometimes locked as well to avoid any backlash on thread that would deter people from buying from them, selling from an autobuy link.
Autobuy links do not provide any sort of tangible security, it doesn't act as escrow for your transaction. There is pretty much no way of getting back your money, otherwise the scammer would not accept this as their payment method.
It's a lesson learned for you. Dealing with gift cards is already risky enough, at those kind of discounts you're unlikely to see any legitimately obtained GCs. There's a reason why DT users have already given negative trust to him ages ago.
