I was hired to produce a website for local gym. When the gym had no corporate identity setup, I offered to submit some ideas. When they chose my artwork, they also asked me to do promotional materials (printed), business cards, banners, etc. When I asked to be compensated for the remainder of what they owed me for the website, they became hostile, though they did finally pay. They requested a bill for the design work and I provided a summary of the services and asked for their input on pricing. Since then, we have had a falling out and they have not only refused to pay me for my design work, they have demanded that I turn over the files and have threatened to sue me. I would like to stop them from using my artwork since they have not paid for it. Do I have any recourse?