First thing I would do is go to your local chamber of commerce (if you are in a town of any size), - also I would suggest getting in touch with your local "better business bureau".
How was the bill paid? If it was a credit card, you have 30 days to "contest the charge", (in essence you can have your money returned). If it was by check, you have a valid recipt that it was in fact paid out, - this can be used in small claims court if you have to!
Also it is possible that you have some kind of "legal aid" (or get a lawyer if nescessary),-that will help you get a "not so nice" letter out to this person, and demand you money back, - -or "to small claims court he goes!" If this is a bad enough job, and entirely proveable,- if you get no results, go to the State Attoureny Genereal! If this guy is a really "rotten apple", - they may rake him over the coals pretty good!
The thing with people that don't really want to make their obligations "good" is that they think the amount is too small for you to really go to trouble to get it taken care of, -and if they just put you off long enough, you will give up! So make sure every bit of correspondence with him from here foreward, is doccumented (in case of court)... you can then show a "trend" -of lack of "good faith" in taking care of the problem.
I you do end up in court, - of course you are going to want to also "sue" for lawyers fees, court costs, and other expenses you have acquired in pursuit of getting your money back, - or getting the problem taken care of! - So you actually get your money back, (and not some token amount that makes it expensive to take to court in first place!)