MTN is *****ing money from my bank account.

Last year October I cancelled my contract with Mtn because it reached the end of its 2 year length. After the contract was cancelled I went back to Mtn requesting that they must please activate the nr. on prepaid because I would still like to use the nr. After 3 days I noticed that the nr. was not reactivated so I threw the simcard away. In December I received a bill via e-mail from Mtn that I must pay them R406. I went back to the Mtn store and asked them why I got this bill. the consultant said that I requested that they re-activate the contract witch I never did and I never signed for a contract. The in-store consultant then told me if they debit the money out of my account then I must just go back with a bank statement and they will refund me the money. After they took the money the consultant sent a e-mail to their billing department and in return they said that I am liable for the instalment because they did send the data and airtime. I told them that I have not used or even been in possession of the simcard for 3 months. They refuse to pay me back and they want to take a another instalment at the end of January. I have been back to the store multiple times but no success.