debiting more money from my account

I've upgraded my contract this year,i was using BlackBerry 9320 and now is z3, the agreement was now they will debit R200 for this phone but now since March they are debiting 258, I went to Vodacom shop where I upgraded my contract, they checked on the system then the lady just gave me number to call(***) I called the number and I was assisted by simo ndebele who said she can't help me until I answer her questions correctly,i asked her which one are you not satisfied with, she just said she doesn't lead clients to answer their questions, she was so rude to me,or its because I'm not a white person? ive just upgraded my contract not to start a contract with vodacom and I've been using vodacom for more than 10 years, what is so difficult to check on why are they taking more money than our agreement? And my phone doesn't use BIS what is that money for? I want my money back. please help patrician madolo