Airtel — postpaid plan change without any information

Address:

Bangalore, Karnataka, 560100

I have been using airtel postpaid plan of rs. 299 (Cug plan)+taxes since 2016 on my airtel number [protected]. Every month i used to pay total bill of 350-370 approximately. When i received the bill this month, it was of rs. 773 including taxes. I was shocked and began checking my usage details. I found that my bill plan was changed to 649 from 299 without my knowledge. I called the customer support and informed them about this. They responded saying that my previous plan had become invalid and it was upgraded to 649 plan. On asking further about this change, they informed me that my plan would be changed to 299 new plan but i would need to pay the outstanding amount. Why should i pay for something which i never opted for? I called them nearly 8 times and every single time, i was assured that i would get a waiver of rs. 400 on my current outstanding amount by end of day. But since last 3 days, i have not received any waiver apart from rs. 150 that i received after my 2nd call. Every time a different person takes the call and i have to explain him/her about all the details, still they don't understand my problem and tell waiver would be initiated within 2 hours or 5 hours or by end of day.
Kindly take some necessary action against this. This is a new trick to rob customers. I would never recommend airtel to anyone and also port my number asap.