Tata Docomo - TATA Docomo Harrassment Threatening Calls and messages

I had a Tata docomo broadband connection for which there was very bad service for longtime around *+ years back.SO i had disconnected the connection but they didnot disconnect it for longtime asking for postpaid bills even if i didnot use it sinc ei already raised a disconnection and waivers. But they didnot listen anything and then closed the connection after * months or so for which they are asking me to pay since that time. They kept calling several times with threatening for arrest warrants by advocates from delhi, mumbai courts etc. etc., emailing me, messaging regularly. I am really upset with all these harrassment calls and frustrated. Email has not come since several daya, but calls/messgaes still continues. I have lost my sleep due to these calls and messages. Please help me on How to resolve and teach a lesson to tata docomo not to harass customers in this manner.