Nedbank is a bully

So nedbank decides to deduct money from my account for a personal loan that I've already paid 18 Dec. When I phone in, am told that its errors that are due because end of Nov, not the full amount was deducted. How do you just decided WHEN to deduct these errors from my account without making any arrangements with me. I arranged that these errors would be paid in Jan, now Nedbank decides that because I bank with them, they will deduct as they please in my account. I want the money reversed back into my account immediately, this stupid agent says he will ask the refund department if this is possible.....It's my money so make it possible. After this, I am closing all my Nedbank accounts and parting ways with them as it's not the first time they deduct as they please in my account.