Same scenario. I did some work for a client who took the work, and basically told me to f*ck off. He added that he was going to change a few details to make the work "his". It was a really stressful situation.

I took him to small claims court and it was settled with a mediator. Long story short, he paid and was told that the funds would be seized if he didn't pay by a certain date.

There is a small fee to file at the small claim's court. Go ahead and use the system, it works if you have a strong case and it will absolve you from the stress and frustration you are feeling.