Indraprastha Gas Limited [IGL] — Issue With the Bill Amount

I received a Bill which has an amount of INR 2771.23 over and above the Bill. When I enquired about the same with the customer service they told me that due to mismatch in the billing amount starting November 2019 till October 2020 the amount got accumulated to 2771.23.

I am not sure why this has happened because the bill generates only after the meter reading was taken by a staff member of the billing team.