Institutionalised theft

I owe Absa money for an overdraft account, which I have been paying off slowly due to financial difficulties. For the past three months Absa has put a debit order on my FNB account for the full amount, which I never authorised, and which amounts to about half of my salary, resulting in my other debit orders being returned, and therefore also resulting in a bad credit record with other companies that I'm trying to pay off, as well as extra banking costs. I have to phone the bank to have this reversed every time, and this is just NOT acceptable.