What are you trying to report a seller for?
Is it the one you left negative feedback for? A case for item not as described will only close if a buyer does not escalate the case in time. If there is no activity it will close in 30 days.
Another for that item cannot be opened with eBay.
For the return of that £8 postage, you could try and ask Customer Services to reimburse you, explain the error in not escalating, worth a shot. Any penalties they give to the seller will not be shown to you.
To Contact Customer Services, I find the quickest way to contact them, either for a Live Chat, or you can select to speak and request a Call Back, to click on this link:
https://www.ebay.co.uk/help/eua?id=5275&mkevt=1&mkpid
On weekdays lines open between 8 a.m. and 10 p.m.
On weekends they open between 9 a.m. and 6 p.m.
@picuk666