Excess Billings and No feedback from Cell C

I'm so annoyed and upset will cell c billings and service. I called the customer support at least 3 times and have also gone in to a store to try and resolve my issue. I have recently moved onto a Giga 20 postpaid package entitling me to a certain amount of data free every month and paying for calls and excess data. This i understand. However Cell C has been charging excessive bills above my contract and usage. I have even saved screen shots of the usage noted by cell c before month end however the bill comes to as much as double and even 4 times the amount stated at month end! Even when i went into the N1 City branch for assistance they were confused at to why it showed im paying for data when i have free data not yet fully utilized. When i last called the support line they said they will log a ticket and get back to me in 2 days after investigating the matter (Ref no: *** and ***). Almost a month later and again no response but i continue to get billed. I feel ****** and regret moving networks.