Company holding my original degree certificate(UG & PG)

I am working as software developer in IT company at chennai, since May 2014. As i signed the contract period of one year and two months as notice period and also i provide my originals as degree and consolidated certificate of UG and PG on May 2014. I have an proof of those certificates are received by company that was signed by the manager. I completed the contract period of one year at May 2015. Due to medical problem(lower back pain) I send the resignation letter to manager via email. They wont accept my resignation and they told you have to work until 31-DEC-2015 and they told a reason as "you signed the contract - only the completion of the project you get relieved but presently the project was not yet completed it is in inprogress". As i spoke to MD regards this, he replayed "I am not provide your certificate until Dec 31 and Where ever you can go not a problem or else provide medical evidence". Since worked up to august 27, 2015. due to medical problem am not able to continue after that and i send the medical reports and treatment details to company. The company does not respond properly so kindly tell me the procedure to collect my original certificate and experience letter from the company. What is the law against the company to take an action?.