Indraprastha Gas Limited [IGL] — I want to complaint regarding the installment igl is charging per month bill

Address:

58 Bal Mukund Khand Giri Nagar Kalkaji New Delhi-110019, New Delhi, Delhi, 110019

My Total installment due amount is RS 6000 which in the starting we already paid 1000 and now the total due is Rs 5000 which is charge by igl on monthly basis 500 per months we are paying bill since 2 year still they are charging their monthly the installment.
Please resolve this because the due amount we already paid if not then let me know what’s is your procedure regarding this.