Continue billing items that are no longer valid

After I renewed my contract with Vodacom, they did not remove items from my bill that were no longer applicable to my new contract. I think they prey on the trust of the public. When I eventually realised I was being over-billed I sent them a series of emails to which they did not respond at first and when I didn't give up they informed me that they have removed these items from my account. I then demanded they repay me these invalid items. There was some non-committal reply from them stating that they will look into it, but so far nothing has happened.<br> What I find totally offensive, is that they made it to be my fault, saying that I should have cancelled these items when my new contract was initiated. This is nonsense. The Consumer Protection Act of South Africa does not allow a company to tie a customer to any form of commitment for more than two years. Anyway, their agents should be properly trained to ensure that the client understands all he is paying for, I would like for them to repay me for these invalid items that they had so conveniently (for them) left on my account.