Here are my two cents:Your first step should be to exhaust all possible avenues with Airtel. Contact customer care and escalate the issue. You can contact the nodal officer of your region. As far as possible, try to get things done over e-mail (even if you talk to someone on e-mail, promptly send an e-mail confirming the contents of the conversation you had with them - because then the onus is on them to deny the same or accept the same by their silence).If that does not work, then send them a legal notice. I don't know any lawyers in Pune, but you can take the help of someone locally.If that still does not work, then go to consumer court. By now you should have all the evidence you need.(Also in case you have decided to disconnect airtel, then send them an e-mail and registered a.d. letter stating that you are disconnecting, and that while the amount due to them is in dispute as per your complaint to them, they should disconnect your connection immediately, and that you will not be liable for any charges for their failure to process your request for disconnection).