Airtel — cancellation of connection/sim

Website:

Airtel service provider

I have moved to USA during October. i went to a nearby store when i was in india during september there was no one who responded properly for the cancellation of my postpaid service.i had to wait for nearly more than a hour and no proper response from any of the representative over there. i got frustated and left the place. later i started receiving bills even after i come back to USA for which i have not at all used. i don't even have the sim. it might have already been deactivated as it was more than 3 months that i have used the sim. still i receive monthly payments from the AIRTEL. i don't think its the right way to charge bills.
In october last week after heading to USA i have asked my parents to go to the Store and request for cancellation. They denied doing it. They said that i should go in person and cancel it. How is it possible for a person who is in Abroad to come to airtel store in india and cancel the service?? when i went in person no response from them. but when my parents went they need me to come and cancel. i even spoke to them on phone stating that i am in usa i cannot come and cancel.accept my parents concern and cancel it if you want any security questions i can answer but they didn't accept . i tried my best. i cannot talk to them anymore i am already frustated. I hate the service they provide.Worst Customer Service ever. i want my number to be cancelled right away and i will not pay the Due for which i have never used.
my number is [protected]. please check the photos which i have attached. i need the postpaid service to be cancelled and deactivate the sim as well.