There is nothing you can do througheBay. Their own money back guarantee only lasts for 30 days. After that, they will not get involved.
March is probably too long ago now even to be able to claim from your payment provider, e.g. credit or debit card issuer.
If your seller is a UK business seller you still have your statutory consumer protection rights - but having rights is not always the same as being able to enforce them. You could talk with citizens advice, they must encounter this almost every day. If the seller is abroad you will probably just have to bin it.
Buying from unknown sellers on eBay is not like buying from known reputable retailers.