Water bill increased by 900% and they can't justify it

They are making up their water usage bill I have been staying in a building managed by City Property and have consistently paid a water bill of no more than R100. However, this month I received a bill of R855 for water- that time I stay alone, and I am always at work When I initially contacted the office, I was told that the amount was due to back billing. Later, I was informed that it was caused by a leak in my unit. After the building manager inspected my unit and found no leak, I was then told that the charge reflects my normal monthly usage. The property manager, Tricha, has been unable to provide a clear explanation or discuss the pro meter reading report. She stated that she does not stay in the unit and therefore cannot account for the usage, which I find unhelpful. Additionally, her approach to handling the matter has been dismissive and unprofessional. I WILL DEFINITELY NOT BE RENEWING MY LEASE!!!!!!!