Ridiculous water billing

I stay in a one bedroom apartment and for the 1st month l moved in l was charged around 420 water bill l even called Protea metering and I was told the water charges increased in June. July it was the same story around 465 water bill , August it even become worse 961 water bill. I did enquire from them and they sent me thier schedule . Basing on that schedule l did my calculation and got to the same amount. Since l was not satisfied l started checking other fellow tenants water bill to my surprise they were paying around R50 and their consumption being 17 kl l tried using the schedule they provide me on how they charge the water and sewage usage but it just didn't tie up. September again l got a 620 bill and sent emails to them asking why for my apartment they have been charging ridiculous bills. To my surprise this month my water bill just went to R45 and consumption being 4kl . When l do the math basing on their schedule it doesn't tie up. The funny part of it is that a person using 17 kl that's my fellow tenant is paying R48 me l use 4kl l pay R45. This just doesn't add up. Up to now they have not yet given a formal response as to why l had to pay ridiculous water bills whilst other tenants at the same complex were paying water bill less than R50.