cancelled contract still being debited

I cancelled my contract effect 31/12/2014 converted to pre-paid. On the 28/03/2015 my bank account was debited by Vodacom for an amount of R235.58. I called customer care spoke to Lusanda who told me she details with pre-paid then transferred me to Mvelo who told me accounts are the one's debiting I must talk to collections. Collection I spoke to Siyabonga who told me he is going to submit a dispute for that amount to Admin and I then told him that I want a refund for return debit charge of FNB which is R138+ he said I must lodge a request with customer care. I spent over 20 minutes on the phone trying to resolve this I find the outcome very unacceptable. I need Vodacom to resolve the matter and pay my bank charges, I'm not willing to get a statements to have to fax or e-mail, it's not my role, they can google how much a return debit costs with FNB and must stop debiting my bank account.