Airtel - Incorrect billing and service denial

I had taken the airtel xtreme broadband connection in the first week of Feb,****. After *Feb,****. And i had made payment for * months initially but my plan was *** per month(with tax it should be around *** rupess per month).
Complaint *) -> Now i expected my * months to be over by May *th earliest and then be billed every month(*** rupees) thereafter. Instead airtel has actually billed me from *th jan to *th april it seems. I had not tken the connection even on *th april, not even in town. Yet they have charged that full month.. *th jan to *th feb.. As far as i remember my connection came after *th feb or at the earliest would be *th feb..yet they cunningly charged the full month and now they are asking me to pay for * months again!!
Complaint *) I have told them i want monthly bill but they will not listen, they want me to pay * months at a time. I have written several emails to them, they did not respond to most of the email but once they responded by saying to change the bill cycle from the airtel thanks app. I asked them how? to show tell me the steps.. because i don't see the steps to change the bill cycle.. i can change bill plan but not the bill cycle.. Then they called me for payment, i told them to resolve this issue first. They said they would do that, but they never did. Now my connection is disconnected after *.* months of usage and full * months payment done to them. I want my money refunded for the half month extra they have charged me already.