Reliance Communications — Charging bill even after the number termination and threatening

I bought reliance net connect dongle with advance rental for 3 months. Payment for the 3 months and the dongle was paid in advance. On 17th may i put a request for the termination of my reliance number [protected]. The request was successfully registered with request no :[protected]. But the employees working on the back end didn't terminated the number and they put the remarks as "customer retained by retention call" despite of the fact that I did not received any retention call from reliance. I am not using my dongle since the day I made the request to terminate the number. But now i am receiving calls from the advocate that a case as been filed against me for not paying the bill. Why should I pay any amount when I had already terminated the number. The fault has occurred through reliance employees not me. Resolve this case as soon as possible because i can not tolerate any kind of bad remarks on my character.