YOU DO NOT PAY FOR RETURN SHIPPING, when the seller makes the mistake.
The Resolution Centre is at the bottom of this page.
As dennis said, open an Item Not As Described Dispute.
The first suggestion (not a requirement, a suggestion) is to Contact the Seller.
You have already tried that so move on.
Ask eBay to step in and Escalate to a Claim.
The seller will be required to send you Return Postage.
If he does not do that, you will be refunded.
If he sends return postage (or a Canada Post shipping label) pack up the item, and return it.
It is necessary that the returned package be TRACKED.
When the tracking shows the item is back with the seller, you will be refunded.
Do not accept an offer of a replacement.
You have to get a returning parcel in the mail within 5 days of receiving the return postage.
You have 30 days from delivery to open a Dispute.
If you have missed the 30 day deadline, you are still covered by Paypal. If that is the case come back here for more advice.