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. Most payment providers offer a 120 day payment protection policy, are you in time to claim there? 4 months is borderline.
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.
@hiretool
