What was the reason for the return?
Was for item not as described then open a case for this citing Item Does Not Match Description or Photos, and enter the tracking number of the item sent back. Once item is received the seller has 48 hours to refund you. If they don't you need to escalate the case eBay step in and force the refund.
Have you followed all of the above? Don't forget to escalate the case listen to no excuses or promised from the seller.
@martinduffyllanmaes