Vodacom please stop billing for something that I don't know

I have been complaining for the whole of September about the line which was added to me without being informed and I got a confirmation email that says that line was now prepaid but to my surprise this line it still shows that it needs to charge me R91 for what I don't know cos to my knowledge pre paid means I have to recharge first in order for me to make calls or do anything this thing its frustrating me too much to a point we're now am starting to hating this network if I need another contract I ll apply for another contract but ant the moment am owk with the contracts that I have