Is there anyone who has had a bad experience with a pool company? (WFUP) How do you deal with it?
It depends on what type of problem.
I assume you've already tried to resolve the situation with the company's management? Until you're more specific about the problem, I'd advise contacting your local Better Business Bureau and filing a complaint.
If you feel they've done something criminal, like getting paid for something and not performing the work, call your state attorney general's office. The threat of losing their contractor's license is a very good motivator.