No reliving or Salary

I was hired by an engineering college for teaching post. After interview they took 1 month to verify my credentials and they asked me to join. I submitted all the original certificate at joining. After 15 days, HR was constantly humiliating and questioned me very much embarrassing about my experience and qualifications. Got disappointed and reached management, they said there was an anonymous letter against me and so they are re verifying things. I cannot be called much annoying in front of the colleagues for this reason again and again. Heard that management wanted me to give resignation immediately. I have prepared and gave it to the principal and left college. He also asked to collect my certificate later. After 5 days went to collect the certificate and others. HR asked to sign some forms including no dues form which mentioned That I collected all the certificate and finances. I refused, but he said it is getting prepared and will give in few minutes. Later, I got only my certificate but not salary nor my reliving order. How do I demand it from them now?