Contract not cancelled as agreed by both parties

My Mother wanted to discontinue a MTN contract last year (2014) and make the number pre-paid. MTN told her to send an email of cancellation, which she did. She then realised after looking at her bank statements that MTN has continued to debit her account. She then made an enquiry in DEC 2014 and it still has not being resolved. Yesterday (2015/02/02) she went to a MTN store and they didn't help her because they claimed that the call centre was closed for business. <br> <br> So her query still has not being attended to and MTN continues to debit her account.