Kerala Water Authority — Unfair water bill

Water bill for the consumer number UPW/2910/D . My mother, Sujatha S is the only person staying at the residence and because of that we usually pay advance bill payment for 6months and our regular bill charges are around Rs 64..But it was a shocking surprise for us when we received a bill of 4624 on 18 December 2020. In the bill it was shown that there is a previous adjustment of Rs.4688. But we haven't missed any single payment . We have only a single tap for the house and there isn't any leakage in the line as well . Again in the following month's bills the payment amount is corresponding to Rs 64 as usual. So I suspect that the bill amount on 18/December 2020 must be erroneous and should be rectified as early as possible. My mother who is an elderly person is having too much stress dealing with this .