Airtel — Mental torcher by Airtel Lawyer

I was using an airtel mobile fone some 6-7 months back in delhi. Then I shifted to bangalore. And i asked for a disconnection that took whole one month. After that I got a call that i have an outstanding of some 1000 bucks and I paid the amount after deducting the monthly rental because i never used the fone during that month. After 6-7 months i got a call that airtel is filing a case against me in Tees hazari court in delhi and if i have to avoid the case then i have to pay some 1600 rupees at airtel collection center. The lawyer is harassing me by repeatedly giving me calls.
Please take my complaint seriously. And suggest me what to do for this.