Illegal termination in IT company

I had been working in IT company for 15 months from oct 2015 to march 2017. I had received performance appraisal in dec 2015 and company was happy with my performance, sincerity and commitment. But to my shocking on march 31st my manager called me and told since you require promotion and you are not happy in present company you have to leave company from today.Company HR told they will pay three months salary.This was verbal communication.As per appointment letter company can terminate me by giving As per appointment letter it is mention the company may terminate your services without assigning any reason with three months notice in writing with a compensation equivalent to your one months salary. My three months salary credited on apr 28. I have filed petition in labour commissioner office in month of june. In reconciliation meeting company's legal hr claiming since i have accepted three months salary I do not have right to claim for illegal termination.As single earning member of family I was busy finding job and rather going to labour commissioner office since getting job was prority.But i could not find job till 20 th of june so i filed petition against company on june 28th. I am claiming for reinstatement but company management is not ready for it. How should I proceed further. How much amount I can claim for illegal termination .Please guide me further