Ebay and paypal money back guarantees are for items that are not as described when they arrive
and not a warranty.
Any warranty is between you and the seller.
If they are business in the UK then contact Citizens Advice for their help.
If overseas or a private seller then there is nothing you can do.
See the bottom of the page on the link where it says
Ebay Money Back Guarantee is not a product warranty
https://www.ebay.co.uk/pages/help/policies/money-back-guarantee.html#receive
