Its possible the seller has been suspended by ebay and the item removed. If so, and you haven't received it, you won't be able to claim from ebay. You need to contact your payment provider about getting a refund.
The other possibility is if you logged in via Google or similar you may have created another account without realising. If so log out, clear cookies and log into the other account.
Or you bought the item while logged out and you would be classed as a guest buyer. If so here is how you check:
https://www.ebay.co.uk/help/buying/returns-refunds/returning-item/returning-items-bought-guest?id=40...