Airtel — airtel is incorrectly charging me on not paying disconnected my connection

Address:

Bangalore, Karnataka

I had subscribed for 6 month airtel broadband connection. Airtel team somehow changed it to 12 month and asked me to pay 5700 more. After raising the complaint 3 months ago no one fixed the issue but closed my ticket. Now they have disconnected my internet. On raising it with team. They agree that its fault in their system. But noone is willing to fix it