I totally understand your frustration, especially when you are being told different things.
In some cases buyers can pay the duty at the time of purchase and in those cases, the duty would be refunded by eBay once the item was sent back. But if you paid when you received the item, the duty can be claimed through Canada customs. If there is a customs form on your package, there may be a form to claim the duty back on the backside of that form. But even if you get your duty paid back, you may or may not get the handling fees back that you paid to the courier or post office.
If you return the item you will get your money back for shipping and for the item,
this is from ebay's money back guarantee:
Currency exchange rate applied to refunds
If a buyer chooses to use eBay currency conversion by selecting to pay in their local currency at checkout, the same exchange rate used at the time of purchase is applied when a refund is issued.
eBay does not cover losses a buyer may sustain that are attributable to fluctuations in currency exchange rates applied to the refund by the buyer's bank, credit card issuer, or payment service provider. If you are a buyer, please check the currency conversion policy imposed by your credit card issuer, bank, or payment service provider for information about conversion rates applied to refunds denominated in foreign currency.
https://www.ebay.ca/help/policies/ebay-money-back-guarantee-policy/ebay-money-back-guarantee-policy?...