contracts renewal despute

I have made it clear on my contract cancelation that I will be keeping the simcards and load data at my own time and I was surprised as I have been billed 500megabytes for R70 for both phones that I am using. This is not what I have agreed on, and what frustrate me more is that their customer care staff keeps on telling me that I am calling the wrong department and give me another number that also I will would be told that I have called the wrong department so I am deeply frustrated , my number is ***.