I think the point DX is trying to make is that, while fraud is obviously a crime, the Police have bigger fish to fry and I doubt you'd get anywhere with them. The same applies to Action Fraud. By all means report the guy, but unfortunately nothing will come of it.
The suggestion DX makes is to request a chargeback via your bank so you get your money returned.
PayPal will then place your account in negative balance, which, provided your PayPal account is pre-Brexit, they can't do anything to recover.
The down side for you though is that you'd need to abandon your PayPal account and create a new one, since any funds that hit your old account would immediately be swallowed by PayPal to satisfy the 'debt'.
If you know the address for service of your LBA and subsequent action, then nothing is stopping you continuing, but do bare in mind, you would require strict proof that you sent him what you say you did.
Do you have that, e.g., a video of you packing up the item? All he has to do to defend your claim is introduce enough doubt that, on the balance of probabilities, the item was either tampered with en route, or you sent him the wrong thing.
If you search the forum you'll see hundreds of threads about a certain delivery company that recently changed their name having packages go missing or their contents tampered with. It is just possible he's actually telling the truth.