Illegal and unjustified termination of myservice

I joined a mnc company as a workman in 1986.Based on my best performance I was promoted to officer cadre in 2008.During my promotion I was issued promotion letter in which there is a clause . the clause says . (This engagement may also be terminated by either of the parties by giving three months notice in writing or three month's salary in lieu of notice thereof.). After my promotion I was not allowed to perform as officer, But I was asked to perform the work which I was executing as a workman.Only my status was shown as officer.I was asked to work on weekends and holidays without any benifit.Since offficers are not entitled for overtime wages. The company is performing good with a turnover of rs 600crores.Suddenly during april 2017 the HR called some of the officer cadre people and asked them to resign or the management will terminate the service based on the clause above mentioned .Since the other people had joined the company as officers and had served the company for few years they resigned and took some amount from the company as excratia and left the company. I my case I had served the company as workmen for 22years and officer cadre for 9years and my remaining service was 5years. So I refused to resign and the management immediately terminated my service based on the above clause. My age is now 55yrs and my qualification is metriculation wit national apprentiship training.So at this age it is very difficult to manage my family. please suggest how to proceed.