If you sent the money via Credit card, call your credit card company and file a charge back. I don't really use paypal but that's what i found on the internet for you
Yeah, there's really no way for then to prove you ever did receive why you paid for. So yeah, pretty much just have a shit fit. At least that's what I did. I've only had to do it once and each time he'd try to deny it I'd do the escalate thing.