Over debited my account

They called to give me a 50% discount on my Absa overdraft then the debited over 3 months based on the 50% discount but instead of them stopping after 3 months they continued to debit for another 3 months and when I call them since last year year they always say that they do see that they made a mistake and they will call me back to fix this mistake after they have spoken to their manager but they never do .I have called they for the past 12 months complaining about their service using my own time and airtime but they simply don't care ....