Marto, you can not sent this buyer incomplete miner. He canceled it a while ago and you ask him for paypal to refund.
Why are you now wonder why hes behaving this way. I agree with bilecinski and refund him like you said.
He did now overeacted but you have responibility for your customers.
Hire somebody who act mature with your buyers.
Its very easy solution, refund him like you stated in december, and he will clean the thread from spams.