Bangalore Water Supply & Sewerage Board [Bwssb] — billing issue

Address: 560097

Respected team,

We have a play school and we don't use bwssb water as we have bore water. For not usage itself initial billing was 500/-, then they charged 1k, then it was revised to 1.5k now billing is 2.5k. On what criteria billing is done. Contacted local bwssb office but none responds properly. Whom should we approach to get the billing issue rectified. We may be using sanitary facility but there should be some criteria for billing.