MTN is not fair

I have been with MTN SA contract for two years and on the process of paying the contract There was ********** on my account with my incorrect information but come the day of deduction additional amount was taken on my account and the case was opened then I made reversal of the ammount charged then I made payment at the branch untill contract come to an end and now due to I want to cancel m told My account is owing as an how I don’t understand I tried calls am not getting help