The eBay Resolution Centre is at the bottom of this page .
While the first suggestion is to Contact the Seller all you want from him is either a Return Shipping Label or an immediate refund.
If he sends neither, ask eBay to step in (still in the Dispute, no humans or phone calls needed) and Escalate to a Claim.
If you then receive the Return Shipping, when the tracking shows the return you will be refunded.
You have 30 days from receiving the garbage, to initiate the Dispute. Five days to use the Return Shipping Label.
The Paypal system is similar, but you have longer to open a Dispute in the PP Resolution Centre which can be found on your PP account page under Tools.
You have 180 days from payment to start a Dispute but you have to pay for the return yourself.
If you back your PP account with a credit card you can use their chargeback system as a third level of Dispute.
But start with eBay.