To start with you can NOT leave neg feedback for the buyer as this option was removed some time ago.

If you leave a false +ive the buyer can get it removed and you cop a policy violation slap.

Call paypal and ask WHY they were not told to return the item BEFORE being refunded and if they do not return your money back to your account you will take it further with the Ombudsman.

Fight it all you can to stop these blasted buyers from scamming sellers and one can assume this buyer has done it all before and knows how to play the system.