First step is to call them or send them an email mentioning disconnection and the reason for the same. As long as you get things in writing, the connection getting closed would be easy to verify from your end.
Here are detailed instructions on closing the connections.
1. Call the customer service number or an email firstname.lastname@example.org or another email ID is email@example.com.
2. Notify them about connection closing. Mention your account number and other required details.
3. Make sure you get ticket number about the issue from the IVR system or from email responder.
4. Keep the print copy of the support ticket.
5. Get the technical to pick up your modem and device and wires.
6. If you have any unpaid bills, then you have to pay them including current payment cycle.
7. Get the document or receipt of your account being closed. Keep the copy of that with you for as long as possible. (There are instances of Airtel sending bill to you even if the account is closed).
8. Make sure you also get the technician's phone number and name, and mention it when you write follow up emails during the connection closer.
9. Keep the communication active till the account is properly closed.
10. After confirmation of closure from both online and offline means, you can get the print copies of that communication.
You have an option to initiate closure of connection using either one of them - email, phone, written mail and by physically going to their service centers.
If you need assistance for the connection closure, just send message to Airtel on these social media channels.
1. Twitter: http://www.twitter.com/airtel_presence
2. Facebook: http://www.facebook.com/bhartiairtelltd
Make sure you keep them in loop on social media if you had any issues with resolution of your disconnection.