How could my bank do this ...

I am in utter shock in the situation that my bank has left me in. IU have been a loyal paying customer for over a decade and now I am in shock. Nedbank personal loans division did not Debit my account last month, I was not aware of this as they always take funds off my account on time. Then this month a wopping R 10 000.00 taken off my account, no warning, no phone call, no email. and now I cannot pay my full rental, all my installments are going to be double next month. Is this treating me fairly ?