Airtel — postpaid bill : excess amount charged consistently

Address:	Hyderabad, Andhra Pradesh
Website:	airtel.com

I have a postpaid connection with airtel plan 499/month. I don't use more than my free calls. As you all know today joi/airtel everyone provided unlimited calls for 150/per month. But i pay 499+tax for limited calls

But airtel charges around 800 last 3 months consistently, and i called them to 121, after speaking to the person they gave me the waiver of extra amount, also i need to pay the bill first and waiver will be adjusted in the next months bill.

Now i just go the doubt and verified the bill last 3 months, all 3 months consistently bill is wrong and excess amount is charged. I dont know how many of my old bills were wrong and i paid excess amount.
It kills lot of time to verify the line item wise bill and call them several times and hang on the call for 10-20 minutes every time.

Is there billing system is wrongly designed or deliberately they adding the excess amount to bill i'm not sure. But whosever using airtel potpaid please carefully validate the bill everymonth before they pay.

Will airtel fix the billing error if it is a bug in their system or stop doing th fraud activities if it delibrately adding the excess amount on top of bill amount