Unfair treatment

I have a revolving credit loan with standard bank and unfortunately in April they couldn't collect the instalment and I didn't know about it up until yesterday where there was money in my bank and they took the instalment for the 2nd time not even on my debit order date and that money wasn't even mine. I asked the consultant why wasn't I informed about the arrears and make proper arrangement for the arrear amount and they can't reverse it. And they have the nerve to call regarding arrears the same day day they decided to take the money on an unauthorized date and I told the lady they should have contacted in April or May and it's already too late for arrangements as they've taken the money anyway. I'm really so ****ed off cause if I knew this in time I would've made proper arrangements.