Bharti Airtel (Broadband) — Adjustment made incorrectly

I have Airtel Broadband Service sice 27th June 2018 and have Airtel Service valid till 06th April 2021.

Airtel has have charged me Rs 55383.68 for this service or 40 Mpbs speed with unlimted data . Even if I consider taxes, there is adjustment missing of Rs 15000/- approx which Airtel Owes me as they have charged me Rs 1500/- per month for this service as against the advertised amount of Rs 999/- per month

I have requested them to check the adjustment for last 3-4 months. If total Payment I have made is Rs 55383.68 and I have to additional pay Rs 300 for the unlimited data till 06th April 2021. I.e from 06th Aug 2020 to 06th April 2021 i.e next 8 months I will be paying 8 * Rs 300 = Rs 2400/- more.

So total Payment I will be paying around Rs 55383.68 + Rs 2400 = Rs 57783.68 for 41 Months of Airtel Service Start Date :- 27th June 2018 and End Date :- 06th April 2021, 40 MPBS Unlimited data costing me roughly around Rs 1500/- per month.

This monthly amount of Rs 15000/- having a Advance Rental Plan for 40MBS speed is not justifiable when the amount should be around Rs 999/- per month max.

I am losing Rs 15000/- which needs to be adjusted