Wrong Debit Date

I'm shocked with the way this company has treated me. I've never banked with Nedbank and I was hoping to move over to them but I'm discussed by the way I have been treated. Last month I called and asked for my first debit order to be on 25th May and not end of April. But they have debit me on 3th May. I'm current sitting with negative of over R5300 and my bank is charging me over R500 for the debit order coz I had no funds and I was not prepared for the debit order. Now calling them to have this reversed and escalated to management, I'm ignoring, calls muted while I'm talking and hanging up on me! I'm really shocked that you treat your customers like this. I would like you to honour the dates we agreed on and my bank charges paid as this is your fault. If I don't get feedback in the next 48 working hours, I will escalate this further!