You fire customers like that. Refuse any future orders from them.
I had a customer once who lost his entire business computer. Nobody could fix it, according to him. I spent half a day on it, recovered the "lost" data, told him he needed to buy a new machine ASAP, and gave him a large bill.
A few days later the machine died again. No surprise to me, which is why I told him to buy new hardware. He wanted his money back. As it happened, I hadn't deposited the check yet, so I mailed it back to him.
He wantede me to return to resurrect his machine again. I demurred and also emailed everyone else I knew in the business to warn them.
I could give half a dozen similar examples. Some customers are not worth having.