Demoted and Pressured to Quit after insisting on receiving Promised Sales Commissions

I work for a major corporation in the Los Angeles area. In my job as a service technician we have opportunties to receive small commissions for sales referrrals (commissions are generally in the $50-$200 range). About 1-1/2 years ago I referred a major new sale that qualified me for about $3000 in commission. Over the next 11 months I had to fight for the commission. The program director that should have authorized my commssion refused to do so. The initial reason was that the paperwork was filled out indirectly. When I produced copies of the correct paperwork, I was told the program no longer paid commissions on this type of referral. It became obvious to me that the company was looking for any excuse not to pay me. The District and Regional Managers began denying that I even earned the commission and began to discredit me to my coworkers and other managers. The more I insisted that the commission was legitimately due me, the more insulting comments I got from my direct manager. My coworkers confided that he, the manager, had it in for me. My manager has lied in work group meetings about committments I have made (with a room full of witnesses that know he's lying). He has shouted at me and tried to blame me for poor team performance. He has slandered me to my coworkers and other managers. He has had me demoted to service a lesser product line and slandered me to my new supervisor.I believe he is abusing me to try to force me to quit. This manager has done this type of thing at least once before when he called a "secret" work group meeting after work and invited everyone but our African American coworker. At that meeting he told the entire work Group of about 12 guys that he didn't like or trust said coworker and was working on getting him transferred to another team. The black coworker is gone and i am fully convinced that I will be next. Every day of the last 11 months have been hell,worrying about job security. After 11 months i received the commission and my boss feels like he lost and has turned up the heat. I am exhausted, can't sleep and just want to leave this job before it kills me with stress, but I can't affored to quit. I am probably days away from taking a stress medical leave and am wondering if I have a case to receive any damages including punative.