You only have 45 days since purchase to open a Dispute, which is what you should be doing.
My concern is that you may have returned the item without Delivery Confirmation. If you did NOT use this, and most Canada Post parcel services have some sort of confirmation/tracking within North America, your Dispute will fail.
It is very expensive to track parcels overseas, $40 or more, so many naive buyers won't.
So. Start with the Dispute. If that fails, go to the credit card you really paid with (Paypal is just a mediator) and phone the 1-800 customer service number. Have your paperwork handy and ask about a chargeback.
Cards have longer deadlines than PP, but they may or may not require proof of return. Some accept proof of shipping others, just like PP, want proof of delivery.