http://resolutioncenter.ebay.ca/
The first step is to contact the seller. You have done that.
The next step is to return the unwanted item to the seller with tracking. You have done that and say you have the proof of delivery.
So escalate to a Claim and PP will probably refund you and go after the seller for their money. There will be other fallout for the seller.
You can leave a Response to any feedback already left by you or the seller. The most effective Responses are calm and factual.
"Returned 15/2/15 no refund"
If you have passed the deadline for a Dispute, which used to be 45 days from purchase, but which loosened up a lot in January, go to the credit card you back your PP account with (PP is just a useful mediator) phone the 1-800 number and ask the clerk about a chargeback.