Calcutta Electric Supply Corporation [CESC] — Higher bill, wrong calculation

From last 1year I am getting wrong bill, visited their office multiple times submitted letter, complained online but no result. My last paid bill was on December 2020 for consumption o[censored]nit 4165 after that present regarding is 4191 as I was not using it but they send average bill without proper reading from my meter box. Now after so many follow ups they corrected the reading this month Jan-2022 but the calculation on amount is wrong, for 26 unit consumption they sent the bill of Rs. 5100. I am not able to pay until they correct this and roaming around them from last year August.