If you open a case with eBay and the seller can proved delivery, you will lose and won’t get a refund.
Mimco I’m not sure what happened in your case but it certainly is not ebay protocol and I’ve never had a similar situation, ever. I’ve always won a not received case as long as I’ve had proof of delivery.
In fact, I lie. Once, in my 15 years as a seller, I had a seller claim concert tickets I sent weren’t delivered, despite evidence to the contrary. I advised her to open a INR claim with eBay and they awarded her a “non fault refund” from their own funds, not my pocket, but in 12 years as a seller, this is the only time I’ve seen this happen.
OP, firstly check the tracking online. It will tell you what Royal Mail depot the parcel was delivered from, check it’s your local one. If not then it’s been sent to the wrong address, so call ebay and point this out.
If you can, check with your postman if he knows anything about it.
Prob the best bit of advice I can give you here is to be nice to the seller and try to get them to push for a non delivery with Royal Mail and submit a claim for compensation which they will generally pay out on if pressed hard enough. The seller can then refund you. Not a lot of sellers will do this though as it does involve quite a lot of hassle, so they would have to be a genuine good egg. It’s worth a shot though, but as I said try to remain on good terms with the seller if you want their assistance.