You are not speaking to anyone from eBay here, we are members like yourself and have no acesd to your account or purchases.
Are you saying the seller provided tracking to show delivery? If so, that is all they need and you cannot claim any refund from eBay, eBay have to believe the tracking information.
If there is no tracking ust the seller saying it's delivered then opeen a case for item not received, escalate on day 4 if not refunded befoehand. As before if the seller has tracking to show delivery, it will close in their favour.
You say it's happened before, this may mean you have the wrong delivery address. On eBay chheckout check this, on the left hand side, before you go and pay, make sure it's 100% accurate.
Also, check you have the correct address details registered on your eBay account, there are 5 addresses to check here :
https://accountettings.ebay.co.uk/uas/addresses