Nedbank Worst Service and Unauthorised withdrawal

This is by far the worst experience of my life, Nedbank withdrew funds from my account without my consent or a bank mandate, when querying it, they cannot assist or it will take 72 hours and this does not guarantee that I will receive my funds, it's not chop change, quite a chunk and my debit orders are all returning, who will be liable for those charges, they don't care, was in the bank several times in Canal Walk, NO JOY WHATSOEVER, What can I do?????