Delhi Jal Board — Bill dispute

We have been charge unethically. The current outstanding bill is 17k however since nov 2019 our bill reading was entered incorrectly. As since nov 2019 till July 2021 the reading entered was zero units and when they generated the of July 2021 they entered the units for the entire duration of 1.5 years. Hence the billing is incorrect. My father's phone number is registered with delhi jal board and he does not check his messages that frequently as he is 74. So was checking his phone randomly and found this bill upon investigating found the error as well so I decided to call jal board but to my surprise the lady over phone told me they can't do anything as it's 2 years old bill.