Misled, over billed and poor network

I took out a contract with Telkom in May 2017 for R139 per month. I was shocked when Telkom debited me R461,83 fr the month of August 2017. I called to inquire of the over bill on 16 August 2017 and was informed that i was erroneously billed the amount and that they will lodge a case to correct the error; the case number given was ********** 0. On 22 August 2017 i received an sms saying my case was resolved, i also received a separate sms saying i must be advised that the charges of add on INTERNET bundles have been credited by the system automatically, no charges on it. i did not understand that sms at all so on 24 August 2017 i called Telkom again and spoke to Nontsikelelo and she told me that i was debited that amount because i don't have a limit on my account so i exceeded my monthly 5G. I was surprised by that because i asked the agent who was selling me this contract which was on promotion a lot of questions based on my past experiences with shady networks and some of the questions were whether i will pay R139 for the duration of the contract and the answer was YES. Should there have been any limits to set i should have been informed on that day and they would have been implemented on the day. I asked Nontsikelelo if my money when my overcharge will be deposited back into my account and she said i must wait for the new bill which will be sent on 01 September 2017, which i have never received since this contract started. Now, i have a budget monthly and Telkom is on that budget for R139 , now i was overcharged by R322.83 which is a lot of money and i have to use it for something else and they expect me to wait for their new bill which will come next moth. It is my first time dealing with Telkom and was referred to by a colleague. i dealt with this "no limit" bill with MTN and i made sure to avoid it with Telkom but it seems this is a way for mobile companies to con customers out of their hard earned money. I was mislead and i want my money back and want to cancel my contract with Telkom. I have had it with these companies taking me for a ride. I'M DONE.