As advised, you can't simply ask Ebay to step in. There is a process to follow.
Provided you received the faulty item less than 30 days ago, you need to start a return:
Use the link, but read all of the details as well so you follow the process correctly.
Open a return request
To request a return, select the item you want to send back from your recent purchases above, or use the button below. You can also start a return request from your Purchases in My eBay.
Start a return - opens in new window or tab
https://www.ebay.co.uk/help/buying/returns-items-not-received-refunds-buyers/return-item-refund?id=4...
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)