Proof of posting is not enough, you need tracking proving delivery.
Returns should be made through a return case and tracking entered. Without that and a case you cannot escalate to ebay. If you opened a Not AsDescribed case and seller had to provide a return label, when it is scanned at the Post Office tracking is automatically entered onto ebay.
The Correct procedure for returns is set out in the Money Back Guarantee on EVERY listing. Not following procedure and you are unlikely to get a refund as seller knows that is the only thing that ebay will accept as proof of return is tracking.
