Unfair Termination

I was working in Private College. Completed my Probation period successfully. One day, suddenly Management issued my Termination Letter quoting reasons for Poor Performance and Feedback. I asked for reasons, they were not able to give. Then they located one email of unauthorised Responsibilities of HOD and told me, asked me what I had done and replied that I had not worked properly. I asked for redressal which was given after 15 days. I have documents related to good performance and positive feedback from Students. Even After explaining to them they refused cancel the termination order. Mgt have never issued any complaint on my performance in writing to me. They are asking me to accept the Order or put up resignation application which I am not willing and get no-dues done. They have stopped my salary dues also and also not paid 1 month relieving pay. Contract at the time of appointment said, either side can ask for relieve with 1 months salary. No new letter of contract was issued after completion of probation period. This is the way they remove Faculties. They threaten them with Termination letter and then get resignation letter signed to cover themselves legally.