Over chaging on my Account

I have a contract with MTN where I get 5OOMB data per month, I opened this contract in February 2015. It is an open line. As per the contract I will pay R399 per month for 24 months. They overcharged me by R2256.6. I have been querying this for at least a month now. I have spoken to 6 different consultants who told me different stories. First they said the date on my statement is incorrect as it was dated 13 October 2012 and they will look into it now they are telling me that the consultant was not supposed to tell me that. They do not want to tell me how I came to that amount. I have asked for a transaction log showing me my spending. Its been a month and I am still waiting.