If you received the item more than 30 days ago, you will have to pursue the warranty with the seller.
If you are still in time, you may be able to get help from your payment provider.
Sometimes, if a seller is not helpful, you can get help from the manufacturer - although that is only helpful if there is a UK contact for the manufacturer, who may need evidence of your purchase or might only help if you bought a brand new item from an authorised seller.
More details would help.
"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)
