Cell c

I have contract with cell c,in January I tried to change the bank account number with cell c,at first I phoned customer care,the couldn't change the account,so I went to the branch in greenacres,to change the number ,they couldn't do it either,so I was told to do manual payment for January,of which I did on my debit order date,sent them proof,now the charged me R70 for the debit order that bounced obvious it will keep on bouncing ,because the account number they have on their system is closed,hence Iam changing,phone them again to query this penalty fee,they gave case number and consultant will call me ,now the sent me an SMS that they have been tried to call regarding the case,so I phoned the call center again,I was told that the case is closed,with notes why ,I'm being charged,I refuse to pay that 70 because I paid on the debit order date,sent proof that reflects the payment date ,It's not my fault they can't change the bank account number,and on top of that no one mentioned penalty fee to me,I was not aware untill I was charged,which means it will be the same for February again because the bank account couldn't be changed .