Billed wrongly

I upgraded in June from a do basic to do premium package. The package includes a 10mb line, 50Gb of data and landline. When my bill arrived they charged me for the 50Gb almost R800. I phoned in and declared a dispute and it got rejected. The next month I went to a Telkom shop and explained to them and the lady helping me said they billed me wrong and had me on the wrong contract. So she helped me put in a new dispute. The 1st of October I receive a call from a lady that is working for the dispute department and she tells me that I have to pay because I used 50Gb. The more I explain to her it is included in my contract, the more she argues with me and tells me she is going to reject it. She then told me she will talk to her manager and get back to me. I am still waiting, in the meantime I see the dispute was rejected again. I refuse to pay for something I am not suppose to pay for