Hi - I returned an item, the seller said they didn’t receive it. I can’t open a request on eBay either… or get in touch with ebay

I got in touch with the seller who was useless, left negative feedback, then they said they’ll refund me if I change it to positive, which I did. And then radio silence from them.

Grateful for any help here - getting in touch with eBay is the hardest part!