Have you opened an Item Not As Described Dispute?
If so, eBay requires the seller to send you a Return Shipping Label.
Which is not possible if the seller and buyer are in different countries.
Call Help and Contact during business hours. You want to get an American customer rep.
Make sure she understands that you are calling from Canada and that Canada is not a US state and is not serviced by the USPS.
Keep hanging up and trying again until you get a rep who is not geographically challenged.
What you want is for the NAD to be closed in your favour and your refund without having to return the item.
Be polite but persistent.
Politely.---- Captain Malcolm Reynolds