Incorrect Billing

I've cancelled my original contract and signed up for a new contract by which I should be paying R800 and some odd for the next 2 years, in October 2015 no problems with the billing in Nov I was double billed called in they said they would correct it this month I was billed R700 and some odd called in yesterday and there is not a single person that can explain to me who authorised the billing in Nov and why my initial query was not resolved I'm currently in credit, my call was transferred from one operator to the next each time having to confirm the same thing and each operator gives you different info waited very long on the phone and insisted for my call to be escalated without any success the supervisor can only call after 24 hrs this mistake will cost me to go into the bank and inconvenience me when they can't run their business right and even if I do this the same thing will occur next month.