Snipped for focus.
I feel like this is a half truth. He likely did pay for prostitutes, and very likely could have stiffed her, and her pimps likely weren't happy about that and threatened him. (happens all the time!).
However, 'deliver them another girl' makes absolutely NO sense to me. He didn't TAKE the first girl (or did he? Is there another dead girl out there, this one a prostitute that no one is looking for?). Replacing one he 'took' (killed?) makes sense for them to want a new one. But it's not like you can pull replacement prostitutes out of your back pocket. Especially a nice girl like Sarah. You might be able to do that with a druggie found on the streets, they could be less likely to try to run off.
Anyway, back to my original thought.... if he didn't 'take/kill' the prostitute, then all they'd be asking for is the money he owes them, not 'another girl'. That part of his statement makes no sense to me.