Collection Company thats threatening me

Good Day I need to lodge a complaint about the collection company A de vos and Norman Bisset, as I was handed over by Std bank to them I was handed over firstly to Norman Bisset not sure if they are working together with a capital amount of 2014/11/15 Capital ' R 17,915.06 R 17,915.06 and I made payments of R18400 and to date they are saying I am owing them 2019/03/11 Outstanding Commission R 551.99 R 9,704.83 which I questioned them on email and on the phone but they couldn't even answer me why is that I could understand collection fees that they have been deducting all along so this huge amount I am querying it with them they now threatening me please help to intervene for me.