Unauthorised data increase

I have a contract with telkom of which I pay R399 monthly and I get 100 free minutes and 1 gigabytes data bundles monthly. If my data runs out halfway the month I call the customer care line and purchase more data. On the 10/09/2015 I got an sms stating that i will be billed for R899 for this month and I don't understand how that happened because I never made additional data purchases. I called the customer care line and I was told that my data limit was increased and I never authorised nor approved such increase and now I have to pay more than double my installment for something that I never requested. I feel that I'm being ****** by telkom and that is unfair. I need to know who authorised such increase and that person should pay for what they did to me