Only delivered half my order

I ordered three items from Yuppie Gadget and when i received the package, there were only two items. I immediately queried this with them, and they said, sorry out packer made a mistake, but we already resold the item so we can't send it to you. This is completely unacceptable given that i had already ordered and paid for it, so i am not sure how they can justify reselling something that is already sold! This is the last time i order from Yuppie Gadet and would recommend that you dont either if this is how they treat their customers.