Overcharged contract

I upgraded at the end of January. I changed my contract to a sim only with minutes and data. It was confirmed by Mothusi Moremedi at Mtn Greenstone. My monthly tarrif would be R469 per month. To my frustration I have been charged R958.83. After calling Mtn to clarify why, I was then tolf that my new contract is inclusive of a device! A device that I did not ask for when I upgraded and a device that I do not have! I went in to Mtn Greenstone to rectify the problem and told that it was not Mothusi's fault, it was the system that just added a device all on its own. Wow, what a clever, sneaky system. either there is truth to this and we have a naughty system changing things whenever it feels the urge or the truth is a bit bent. To add a cherry to this wonderful debacle, I was told it will take 14 days to refund me my overcharged money! Really!