With no access to your account it's difficult to see what has happened here, but could be one of two things.
Did you perhaps buy the item as a Guest Purchase? Then, nothing will show in your eBay account as it wasn't used for the purchase. if your item doesn't arrive, this will show you how to receive a full refund.
https://www.ebay.co.uk/help/buying/returns-refunds/returning-item/returning-items-bought-guest?id=40...
Or, if you did use your eBay account and the seller has breached selling regulations, eBay will remove them from their site. Here, you'll need to contact eBay Customer Services to open any case you need.
This is the easiest and quicket way to contact eBay Customer Services, for a Call Back option.
https://www.ebay.co.uk/help/eua?id=5275&mkevt=1&mkpid
Lines open between 8 a.m. to 10 p.m. on weekdays.
9 a.m. to 6 p.m. on weekends.
I recommend contacting CS very first thing in the morning, when the lines first open, as there's more chance of Dublin answering.
@thomablazeb_0