How do I file a complaint against an employer

Hi, Thanks for taking time to read my case! I am working in a USA IT staffing company since last 6.4 years. Four months back they have requested me to handle our new branch in Bangalore location...after working for one month my health has started giving hard time and requested my employer to hire someone else to replace me; for that they were not OK and asked me to continue there only. As my health was not supporting i did not find any other option than resigning from my job giving 3 months notice which is a must as per company policies. The employer did not accepted my resignation and my GM came with a proposal saying they will allow me to work in home branch(Hyderabad) in case if i withdraw my resignation. I happily accepted the proposal, came back to Hyderabad and working from last 2 months. But now the company has terminated me without any notice or reason, and the CEO has used abusive/filthy language against me and threatened to beat me up and the company has denying to pay me Severance/Gratuity/PF. I never acted against company policies nor used any incorrect language nor misrepresented in any manner...my reputation among the team is very good and I did not had single negative remark in my whole tenure. Could you please help me filing a case against my employer. Thanks & Regards, Johny