You cannot report this to eBay as they do not offer warranties or guarantees on items, just that they are just as described on receipt. If they are not, a buyer has 30 days under eBay's 30 day MBG, Money Back Guarantee policy, to return the item for a full refund.
If you bought this from a Private seller you are too late to claim a refund. You could try your payment provider for help with a refund, now.
If purchased from a registered UK business, who offered a guarantee and is now not upholding this, then turn to Citizens Advice for your next steps, if you wish to take this further.
eBay's 30 day MBG, Money Back Guarantee is written on the right hand side of every listing, and here on the link below. Familiarise yourself with it, it could save you a lot of money and time in the future, as promises from a seller can be broken, as you've found.
https://pages.ebay.co.uk/ebay-money-back-guarantee/
@elaines518