account management

I am a prestige banker at standard bank, every-time I swipe the balance go of the account and my account balance decreases which I right. But the after a week I see my account going into overdraft. And I don't have a overdraft. What balances goes of afterwards as every time I swipe I get the notification and my balance reduces immediately. So I don't understand I am going to close this account as the other banks offer a better package anyway.