Airtel - Airtel promised to change bill plan and then over charged me

*. Last month i.e in April ****, Airtel representative called me and proposed a new *** unlimited postpaid bill plan and told me that the plan would change in ** hours. At the end of the month, I received a bill of Rs. ****. When i called the customer care, i was told that my bill plan was not changed and I was charged as per the old plan.
*. I had to call repeatedly to the customer service because they would put me on hold and after *-** minutes, the call would drop automatically, this happened * times in a span of one week.