Misleading marketing and theft

I was contacted by Cartrack on the 17th January regarding a button they wanted to activate on the app on my phone. As I am a new user, I did not realise this was for an additional service at an additional cost as this was never mentioned. It was only on the 19th when an amount went off my account that I realised there was a fee. I immediately contacted Cartrack and informed them that I had not agreed to an additional amount on the current contract. I kept getting emails and calls asking when would be a convenient time to deduct R50 cancellation fee. I told them as I'd never agreed to an additional amount, I did not see why I needed to pay R50 cancellation fee. I must have spoken to at least 6 different people from different departments telling them the same story. They totally ignored me and deducted the R50 cancellation fee on the 31 January. It might not seem like a lot of money but they have '******' just over R100 from me.