It certainly wasn't done via AW - someone's used some software to make the text appear to come from 'adultwork' or whatever it said. Depending on the voices, you've either been dealing with just one guy as client, 'agency', and 'adultwork' or two - if it's the latter, they probably swap who is going to get the free sex each time.
As with everyone else who's been scammed into doing a freebie, he has committed an offence but you're never going to see the money and you will need more than just you to get the police interested. But I bet you're not the only one this has happened to, because there's no way something this elaborate is a one-off.
Don't delete the texts, post the number here (with the last two digits replaced by *s, of course), and report it to Uglymugs and the London sex work projects.
Did you ever go to the 'office'? I bet it's an accommodation address.