Had you done the return request through ebay the seller would have had to pay the return postage. If you sent the parcel back and have the tracking number which shows the parcel as delivered you can call ebay to ask if you can still open a case for not as described. If they say no then open it in Paypal and when they tell you to return the item give them the tracking number.

If you did not keep the tracking information there is little you can do as you have no proof that you returned anything.