Not restoring old overdraft limits

On Wednesday 24 November 2015 I went into my online banking settings and wanted do decrease my overdraft limit and made a typing error and reduced my limit too far.I immediately phoned FNB but everybody can't help me.I was reffered to my private banker.I explained to her what happened and that I need my old overdraft limit to be restored and she told me that I have to reapply for a overdraft and I might not even get the same amount like before.I said to her that it is not fair that I have to go through the whole application process again because that I was approved for that amount and I just want my old overdraft to be restored.My debits is going off tonight and my account is in the minus.I have been with FNB for 15 years and if they can't help me with this then I am going to move to another bank.Why do we have private bankers if they can't help you when you really need them.