Overcharged

I have a contract with Cell C.<br> Last year Oct 2015 I was legible for an upgrade. <br> I upgraded from a BlackBerry to a Samsung.<br> Samsung does not have BIS (BlackBerry Internet Service). A service I paid R50per month .<br> Henced I purchased 1gig of data of R149 monthly to use the internet service excluding my subscription fee on my Samsung. This month I checked my itemized billing and saw that I have been charged R50every month for my BlackBerry BIS . A service that became nul and void since my upgrade Oct 2015. Contacting Cell telephonically redarding my query. Im being told you should have deactivated the service. Since it was a value add from cell c ( to me a value add is free) there is no credit owed to you.<br> \I'm deactivating the service now so you won't be charged again next month\". R350 I will not get back? I requested to speak to a manager