Ebay needs a good reason to step in and cancel a sale: if this happened, you can be sure they did you a huge favour as disappointed as you may be that you did not get to have whatever it is that you won at that price. It would not have come, as it likely never existed.
If the seller cancelled the transaction, it is better to be satisfied that you got your money back from paypal than to have received an item that was not as described in the listing. Sellers are not supposed to renege on completed sales but sometimes they do and there might be a variety of reasons for that. If more than 60 days has passed since the transaction took place, you won't see it anymore to leave feedback.
