Pre-paid credit disappearing

For the past 3 years I have been a pre-paid client, enjoying excellent service. Up to about 10 days ago, when my credit that I loaded suddenly disappeared. I recharged with R150 and used about R20, then suddenly it disappeared. I recharged again, used about R30 and the balance suddenly disappeared. I do not use my phone for data as I have access to Wi-Fi. The feedback that I receive from customer service (which by the way the 084135 number does not exist) from a store in Greenstone Mall, tells me that I have used my credit on data and claims that they can prove it. I have requested the report but have not received anything. I would like to get feedback that makes sense and for this issue to be resolved, otherwise I will have no option but to take further action.