Me personally I wouldn't put anything in writing he can use as evidence to show its sex work related, in case he does try reporting it as sex work to get bank to refund him. Coukd you send him a vague text like I not sure what talking about please call me.
Maybe Then tell him politely but firmly he made the booking it was his decision to leave early through no fault of the experience being delivered. And that he should book the time he intends to stay for. And refunds are not avabut on this occasion only you would give him a half hour appointment on x day (of your choosing) . If he's not happy if he can fuck off, but nothing in writing.
I had a client try and pay by cc recently but I had a feeling he was going to be a snide straight off, told him cash only. There's some out there that do this to get free appointments, obtaining services by deception but not so to the police as its against terms and conditions on banks, whether its card payments, transfers. Even though said client planned it.
Don't refund him your turned other work away, not your fault he's a cummer and runner.