Bad treatment, bad service

I have a homeloan with Nedbank, they collect the monthly installments via debit order. My installments are R11,700 per month I have never skipped payment. On the 6th they collected the debit order and debited an additional R7000 imagine! I have called them regarding this, they told me that the amount will be automatically reversed. it been 3 days my account is still overdrawn by R7000! thi is ridiculous. really what am I supposed to do?