Extreme data over charging

Last month my accounts and Internet was suspended. Upon inquiring I discovered that I had used more than my allowance and had been charged an additional R 1000. I queried the charges and was told that once my data allowance was up they would charge me at the out of bundle rate. I asked why I had not been notified and told of this. I paid the bill and resolved to turn off my data so that I would not suffer the same fate. This month, however, has been worse. I have just xperienced tha same thing with an even higher bill. I cannot account for this amount of data as I have turned off my cellular data when I am not using my IPad. I cannot get hold of the call centre and I am devastated at this extreme amount of money. What do I do?