Got RPAD Letter From Company After Leaving The Job

I recently joined a company 1 month back , and I worked there for a month. I had to face lot of problems from my senior staff in the company and used to insult me in every way possible . And also I got the job which I was not promised for and I had to do duty shifts which I was not comfortable with .I couldn't tolerate and I wanted to talk my problem to the HR department , I gave a appointment letter to meet them , still they were busy , and once I met the administrator of the company on the way and told , he said he will look into the matter , after that there was no sign of changes in my duty and no help I got from HR department. I also made to sign an agreement before.( Not a stamp letter ) . After all these , I had left the job , and sent a mail to the HR department, now I got a letter to home ( under RPAD) from HR department , that I need to go to that company with written explanation without which they can proceed against me in court of law. Sir , what should I do now !