Telkom Contract over billing

My husband and I have two contract with Telkom ,on the month of February we received a bill stating we owing R603,700 because we had exceeded the limit which is 12.2 gigs .My husband went to Telkom at mall of the north Polokwane to inquire about the matter , he was told that we exceeded the limit on the 10gigs sim i am using, so he was told to connect the sim on the phone and type *180# and to choose option 6 spent limit R1.00, which we did.The month of March I reached my limit and i could clearly see the message on my browser saying I have reached my limit and i will need to purchase data to use the internet. I left it as it is. because i didnt need it, and there is only 5 days left for month end and the next month data will kick in. now to my surprise the bill has increased way beyond my imagination. last month they said i used 12.2gigs we paid R603,7 this month we used 12.9gigs , the bill went up to R964,00 yet i had set the amount to R1.00. We are being over billed every month .We thought there was hope for Telkom but if this issue isn't resolved, We will take our business to other network provider and never recommend Telkom to any of our clients as this is an unnecessary issue which just causes frustration more than anything else. This leads to many people changed from Telkom to other provider simply by word of month which creates a bad brand reputation.