Unauthorized Debit Order

This morning I received a sms from my bank that an amount of R570.50 were deducted from my bank account for Vodacom. My Vodacom premium is R105.49 and this were deducted on 23/08/2015 already! I phoned customer care line and they informed me that my OLD number were given to somebody else and this amount is for that persons account with them. My old number were used again by somebody else and I'm paying the account, how nice is that? To make matters worse is the fact that the lady told me that I need to go to my bank to reverse the debit order. They can deduct money from my account with out my authorization but they can't refund me my money! My funeral policy could not go of my account because of insufficient funds and my bank is penalizing me for this as well. How can Vodacom deduct money from my account with out my signature or my consent?