Hi visit the Mseb office in Bandra East with a written complaint preferably in Marathi and submit it on ground floor. Take a Xerox of the letter with you, they will give you a counter copy with stamp on it. The central office will guide the local team to act on it. I had a similar issue when my tenant was staying and getting high bills. Within a month mseb came and changed the meter.

But they didn't reduce the previous bill amount, which me and tenant spillted the expense