Billing after cancellation of contracts

So I just got a call from Moses in the customer Care department and the more I try and explain that they billed me for failed Debit orders that I paid EFT before hand he kept telling me that it is not possible I have sent all my proof to Cell C and made numerous calls I then asked him to put me through to management and he advised that everything starts and ENDs with him, he also said that he can say he is part of management and when I asked if he is management or not he said no he is not - he said that he is handling all the queries and when I asked to speak to his manager he said that his manager will tell me the exact same thing that he is telling me I asked again to speak to management and he advised that I need to call the customer service and ask to speak to a manager but he is in customer services just under the social media side it is the same thing. He does not wait for a person to finish explaining their side and just keeps on talking so obviously you will lose your temper it is getting worse and worse the more you speak to Cell C. I do not want a normal level employee to contact me I need to speak to management alternatively I will seek out the "BIG SHOT" and get in touch with them directly - I have my own means of tracing as I have been in the industry I know how. so get a manager to contact me.