To comply with eBay's buyer protection porocess you have to return items via their system. They only go by that trackable proof that an item has been sent back.
You could try contacting ebay about it. I can't really see what they can do but it's always worth a shot. You can ask them to ring you here:
https://www.ebay.co.uk/help/eua?id=5190
You could also contact your payment provider and ask them about a refund or chargeback.