Please note if terms and conditions mention that you have to serve one month notice period you need not work after 16th March 2018. If they do not release you or give experience letter you can send legal notice stating that in case of damages the manager and company shall be liable to pay existing and future losses incurred by you because of their acts. But if the terms and condition state that you need to work after serving one month notice or till suitable candidate is found in your position then they have right to hold you back. Better send a legal notice through a local advocate asking them to release you on march.