This is my response:
I am writing this since you put it out here. My advice (which you can throw in the garbage if you want) that has worked for me: Call them.
The agency that you went through that had booked this non-paying client, the client who "pulled a fast one" like you said, and anyone else you can think of. Call them several times a day. I mean on the phone. Call them persistently and be pleasant.
I have had companies sic their lawyers on me when I do this, and I have no problem with it. You are in the right.
I know this may sound mean, but complaining about it on Facebook might be emotionally cathartic, but it won't get you your money back that way. Just my 2 cents.