Handed over despite arrangement with bank directly

I have a personal loan with ABSA. I made a payment arrangement earlier in April this year to pay a reduced amount until my financial situation improved. So the personal loans collection department was already aware of this and that the account would be in arrears.

I got a surprise call from a company called Nimbus Debt Collection last week saying I was handed over by Absa for missing a payment.

Now a few things I have made me irate about this whole process:

1) No one from ABSA called me to inform me of a missing payment. I would think this is standard practise.

2) I have never heard of a policy where an account gets handed over after missing one payment. I can understand if it is 60-90 days overdue and needs to be handed over.

3) After calling the collections department about this on Friday 6th October, I am told I need to call a complaints number if I want to make a complaint about the process.

Whatever happened to understanding the situation first before telling a client to go phone another number? There seems to be no common sense being app****.

I want my account to be taken back from the legal department as I had an arrangement in place and I want this addressed urgently.