Taking money for No Service

I have upgrade Mid April 2015 at Vodacom Centurion Mall - I upgrade from a Blackberry to a Iphone 6 - On the day I asked them and even filled in the form to cancel my BIS for my Blackberry - Since then they still charge me every month R51.75 for the BIS fee - I would like this cancelled and would also like this over paid money paid back to me - The good service Vodacom always had - is slowly but surely going down the drain