Honestly pretty shocked at the responses berating the OP for spending this money. How many of us are in a financial situation in which we can just tuck three grand away and leave it there, in the name of Good Business? It's WILD to me. So many of us, in fact, most of us I would say, start doing sex work because we are in a place of financial precarity and for MANY of us that financial precarity DOESNT GO AWAY. The OP is clearly a person who struggles with mental health which can affect her ability to work, and I would hazard a guess that she probably isn't in a a position to follow all of these rules. Of course in a perfect world we could all do this, and I'm glad that so many of you seem to live in that perfect world, but it's not like that for everyone. To everyone who wants to berate her for spending the £3k, if you were in a situation where it was 'spend a prepaypent or be hungry/fail to make rent and become homeless' what would you choose? Jesus christ. And honestly, 'what if he wants to book someone else with that money'? Really? His potential penis emergency is suddenly more important than one of our own, who is clearly having a tough time right now? She said shes going to pay him back. There is NO need for this. A bit of solidarity wouldn't go amiss.
OP, I'm sorry you're dealing with this. The clients are generally in a position of power in this industry, what with having the financial upper hand, and us relying on them booking in order to pay the bills. I understand his annoyance about this but you're not trying to run away with the money you are offering to pay him back in instalments. A court won't touch this AFAIK and if they did all they'd do is take instalments from you also - nobody can take money from you that you don't have. Sex contracts aren't enforcable in court and if he lied and said it was a loan, depending on your circumstances you could tell them the truth that it was a sex contract. He would need to show proof anyway and if all he has are texts to a potential sugar baby they'll tell him to fuck off.
I would suggest writing him an email making him an offer, clearly laid out of how much you'll pay him and when, and when the debt will be cleared. Tell him that you have absolutely no intention of running away with his money and that you are deeply sorry for how this has turned out, but that you can't give him money you don't have. Echoing the other suggestion of perhaps seeing if you can get a loan or a credit card to pay him off and then you'll just have to deal with the company instead of him.
Good luck and take good care of yourself. xxx