I think someone had an issue like this before...I think that there are some glitches with their site...? The person lost out, but she got refunded. You must contact them asap. I'll keep my fingers crossed.
I think he lists everything on let-trade as well as ebay and whichever site he sells from first, that person gets the item. Its really confusing that he does that but I guess its just more marketing and exposure for their company.
IN the future, for everyone's reference, your best bet would be to get their phone number through their FAQ page and call them. Asking on TPF won't help much since like lilirose said, we are not let-trade!