You could research the business name and address to see if there is a phone number or write the seller a letter explaining your issue and wht you expect them to do.
After more than 6 months, your rights are limited but if the seller provided a warranty, you could ask Citizens Advice what 'next steps' you could take.
"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)