Telkom opening lines and robbing people.

I had taken a data contract with Telkom , which I have been paying R99 for the almost 2 years. recently I got debited R600. when I contacted Telkom they say I went over and my line was opened and I have never received commutation that my line was opened and it was never told to me when I took the contact. In the past when my data got finished I always bought . when my data got finished for the past couple months I was unable to buy data and I could not use the modem. Is Telkom trying to rob customers. I am really upset with this service and I actually regret taking this service. I don't receive monthly statements and I never opt for a open line and Telkom wants to rob people. I always thought that Telkom was a good service but after this experience i an very unhappy and i want to cancel this contract with them .