I bought some GHS for CEX.IO just to see what it's all about and it's pretty cool how it mines BTC, NMC, IXC, and DVC all using the one amount of GHS (so 1GHS mines 1GHS on all of those, doesn't divide it between them all but each one gets the total amount) anyways, that's besides the point, I ended up earning enough DVC which I have no idea what to do with becasue there is no trading DVC or IXC on CEX.IO.

I made a listing on eBay to sell 1.0 DVC as a CEX.IO Voucher and I sold it, got paid, gave the person the voucher code, and now they're telling me it didn't work. They're telling me the code was invalid but I just made it so I think I'm being scammed. Is there any way for me to see if the voucher was accepted and maybe they're just saying it's invalid so they get their money back?

I told them I would issue a refund as soon as I can confirm that the DVC was actually invalid because 1.0 DVC is now gone from my account and they're asking for a refund and I don't know what to do to prove that the voucher I gave them was valid unless I can prove it was accepted and they're just trying to scam me.

Any ideas? I tried contacting CEX.IO but they said all voucher transfer status is private for security so I don't know what to do from here.