DJB — complaint against wrongly generated bill

Myself a customer of djb, ca no [protected]. Water consumption of my family per month is less than20kl. That is why i got 100% exemption on water bill till last month. My current meter reading (On 24/9/2019) is 576/ok, and previous updated reading was 258/ok (On 13/07/2016).
Hence my total consumption is318/ok during last three years. Djb recently send me a message stated bill an amount of rs 816.
Please take a corrective measures in this regard and oblige me.