EBay is only an online marketplace, where sellers can market their items for sale.
EBay itself doesn't sell anything, and takes no responsibility for items sold here beyond its own, 30 day money back guarantee. From day 31, eBay has no further interest. PayPal buyer protection, where applicable, lasts for 180 days, but only covers non-delivery or faults that are present on receipt. Neither will get involved in faults that occur in use, or in warranties.
Otherwise, any responsibility rests with the seller. If they're a UK business seller you have your statutory consumer rights - although enforcing these against distant eBay sellers who don't want to know can be difficult or impossible. Even manufacturers' warranties are liable to be invalid for items sold here.
You can consult trading standards or citizens advice, or consider using the small claims court or the Courts and Tribunals internet-based money claim service: https://www.moneyclaim.gov.uk/web/mcol/welcome.
It the seller is a private seller, or abroad, there's nothing you can do.
Good luck, but buying from unknown sellers on eBay isn't like the shops.
