What do I do if I've been threaten with terminated if I continue to seek assistance for a supervisor who mistreats employees.

I've been an employee for this company off and on for the past 19 years. In the time I've been working for them I have resign twice for wrongful treatment. I'm currently working for them again and I went to staff relations as I have in the past for wrongful treatment by my superior. When I first went to seek help my representive was supportive and sent me to several agencies for assistance. Now she not supporting anymore and revealed to me today that if I don't back off I could be fired. She also mentioned today that if I don't like what's going on I should quit. I have left my last two position at this job at this company for the same reasons and I've lost thousands in salary. The stress I have endured from this job has case medical complication and I've been hospitalized twice.