Billed for BIS on a contract with an S3 Mini

I have a top up 100 contract which came with a Samsung S3 mini. The contract was taken as an upgrade with Nashua in October 2013.<br> When my contract was transferred to MTN, in December 2014 BIS High was added onto my bill at R51-75. I went to the Chatsworth branch and I was assisted in removing it from my bill (Ref***). I was still billed for BIS the next month. I called 808 and I was told I had to prove that I don't have a blackberry. Nashua didn't give me any paperwork. Today I went back to the Chatsworth branch of MTN and Navashni and Manisha were no help at all. Manisha told me that I'm being charged BIS as my previous contract with Nashua was for a BlackBerry therefore it's a value added service that was always there. I asked her to please explain why I wasn't charged for this service when I was still with Nashua. She then tried to justify the extra charge was for hardware fees after seeing H/W fees on my bill. I then pointed out hardware sub on my nashua bill for the same amount. I asked what about the Jenga service fee Bd 250mbI was told they cannot remove it as it is a third party application and I have to do so on my own. I didn't subscribe to anything. Please assis