Airtel — unauthorized charges to my bill

Address: Panchkula, Haryana, 134109

Airtel changed my monthly plan on their own without any communication to me. As per them, they gave me waivers as i was a premium customer to them but then without any intimation they increased the rental. Now they are asking me to pay double the amount which used to come as the bill.

Following are the details of the plan month wise starting march, 2017

March - 1380
April - 1380
May - 1472
June - 1725
July - 1788
Aug - 1888
Sept - 2488
Oct - 2488

This month bill was generated with 3005 as my rental and i paid just 1500. When i called airtel customer care, they just said that they can waive off 500 and i will have to pay 972 more. I dont understand the reason behind that. Why would i pay the company without any reason.