Previous Company holds my original certificates

Hi, I joined an IT company based in Chandigarh in October 2013 and I performed well during the time period of 6 months. The reason I left that company is because my immediate manager was keep restricting me talking to other colleagues as we are a team of two only, he always took credit for my work as well and defame me in front of team manager. Even on complaining about him no one listened to me until I resigned from there. At first, they were not accepting my resignation either and forced me to stay just because my immediate manager kept saying that there was a load of projects and so, but there weren't any projects that time. Then, After resigning I served for next two weeks and requested them again and again to relieve me as soon as possible. The manager literally made me cry and laughed on me in front of all. When I left, The executive HR told me that they will give my document back to me later on and I started the job in Pune after that. I came very rarely back to home and whenever I came they always gave me a list of excuses of meeting and busy schedules. Now, I contacted them again and they are saying that staff is changed and new ones are not ready to give my document back again and they are asking for compensation or they will take legal action against me. I didn't sign any bond but there was a contract stating at least one-month prior notice. Iw as ready to serve one month but they were not ready to relieve me even after one month. I really getting so stress for this. Please guide me as appropriate. Thank you. Best Regards, Nav