Company forcing me to Serve extra month after serving the full NP

Hi There, My Name is Rabi and I work for an IT company HQ based in Chennai, I asked for relocation to Hyderabad on February 2017 which is why they made me sign a service Bond of 1 year associated with a penalty amount of 2 lacs in case of breaching the bond. I dropped my resignation on 13th July 2017 and as per the company policy I am ready to serve the 2 months of notice along with ready to pay the 2 lacs penalty. But till today they are playing around with me on my release date which should be 12th September. They also have said I have made delayed in responding to there email agreeing to the terms in the bond, which is why I have to serve one more extra month of Notice period. I have my joining in my new organisation on 15th September and serving one more month will make my new offer rolled out. I also getting threatening that if I bother them with this then they will terminate me and update bad remarks in Nasscom. I have tried to speak everyone possible in the company but no one is helping me. I cannot join my new organisation without the reliving letter and also if I couldnot join by 15th September they will roll out the offer. Please advice. +[deleted]. Thanks