Customer Wants Refund But Not Followed Manufacturers Instructions

A customer bought a clay chimenea from us last week and upon first use it has cracked. From photos provided by the customer and information provided by the customer it is absolutely clear that the customer hasn’t followed the manufacturers instructions to “cure” the chimenea before using properly for the first time and so the reason it has cracked is his fault. I’ve fed this back to the customer and he’s now pushing back saying “I’m taking this higher I want my money back”.

The customer has previously opened a Return request, but as far as I can see hasn’t yet opened an A-Z claim.

The value of the sale was £95

Any thoughts / suggestions? I’m assuming if he did open an A-Z I’d lose automatically so do I just give in? Ask the customer return it as per the Return request (even though it’s useless?)

Thanks