Debits account without arrangement

Nedbank Personal loans just debited my banking account without prior arrangement and took all my money in my account.I am not sure how they could do this and how they expect me to survive till month end? I told them last month I will only be able to make an arrangement as soon as I know what my total income will be at the end of this month as I started a new business. They have put me know in financial difficulty. I will have to close all my Nedbank accounts as they not making things happen. Very dissatisfied ex staff member. They also increased my interest rate from prime to 28% I understand when I was employed with them I received staff rates but an increase of 18% + is ridiculous. My affordability at this stage not taken into account.