Airtel — daylight robbery by airtel by giving false certification on 4g plan

Address:

560043

MY handset is not 4g compatible as per Airtel network so the plan i took for 84 day's (1gb free every day, unlimited calls) was cut short to 35 days.
My phone is 4G - LTE but not as per their specification it is not.

What should i do?
I paid 500 for 35 days connection instead of 84 days! This is ridiculous!

I want a solution to this as Airtel customer care does not bother provide any support to extend my plan to 84 days! I dont understand how difficult will it be to extend it for something that I am supposed it. Should i take this to Head of Airtel?