Telkom fixed not fixed

Telkom has the poorest client feedback and assistance I have ever encountered as a Quality Manager. They do not have a system in place to assist in sorting out a problem. I have a Smartbroadband Wireless FIXED 40 GB monthly account with them for R459.00. During April my kids went over the 40 GB and they charged me R4300 for 70993 MB. As I wanted to know why did they charge me and did not cut off my data as we went over the FIXED 40GB the lady at Telkom told me they did send a message to warn me, which I did not get and not gave my consent that they can charge me. The second time I called they let me know that it is not capped...… so what does fix mean? These little facts they leave out when the promote a contract that sound so wonderful. So after holding on for hours to speak to a consultant twice no one called me back and my line was cut. I am NOT going to pay the R4300 for 70 Gigs. So who do I speak to with authority???? Major non conformance.