If you have an Unpaid Item Claim open against you, you will have to answer the dispute within the claim.
Give the Paypal transaction number and ask for a refund.
If you offered to pay by cheque, cash or money order, you have just learned why eBay warns you not to do that.
If the seller demanded payment by cheque, cash or money order, he broke an important eBay rule. Enter the eBay Message into the dispute and it is very likely you will win.
But unless eBay decides to refund from their own pockets, you will not get back money you sent untrackably outside the eBay/Paypal system.
If you paid directly by credit card, contact your card's customer service.