Airtel — Misuse of ECS after SIM cancellation

Hi All,
I had a bitter experience with Airtel. Airtel took 2 months to act on my cancellation request and in the meantime abused the ECS facility and deducted the bill amount from my credit card for 2 months. Finally, I blocked my credit card. My repeated requests to their Customer Service desks fell on deaf ears. Their zonal officer cannot be reached on the number provided in their website.HDFC bank told that they cannot cancel the ECS as it was directly between me and Airtel. Airtel Customer Service centres were not ready to accept the cancellation request for ECS and informed that it is a tedious procedure. Pls. let me know on the possible course of action that i can take.

Thanks