Nedbank awful service

I have been banking with nedbank ever since I opened my first bank account over 20 years ago, I have since taken numerous loans and paid them up, however last year I was pregnant so went a bit off with my finances and have since been trying to get back on track. My loan agreement expired end July, I made arrangements for debit order to go off end August however as soon as my Sars refund went into my account a few days ago, nedbank immediately debited my account with over 3000, I had commitments for the money and requested a refund only to be told it has been declined, I contacted the complaints department who said they will respond within 24 hours, it is now 2 days later and no response, when I tried calling on the Saturday they said they are short staffed, called again then got told to call back on Monday because the complaints department is not available. So I have spent my whole weekend in agony. As I understand it if my loan term expired they do not have authorization to just debit me whenever they feel like, the fact that you had the account for years and years and numerous loans and never defaulted should count for something, I can open a new account if I wish too and pay them 500 instead of 3000 but I want this paid up as much as they do and I'm making regular payments. Its not fair they can just debit you after you made arrangements and then refuse to refund you.....