Horrible customer service

I sold their car to webuycars in October and we agreed that I would pay off the shortfall in installments. I was allowed Thapelo Ncubula as an assistant. So in December which was my last installment I got paid on the 17th, so I decided I wanted to settle the debt ,so on the 19th I called Thapelo Ncubula 3 times without any success, I called the customer care,I was told that they were forwarding my call to him, and at that time am using my air time and I've already answered questions, I couldn't go through, I had to call again and still had to explain my story and taken from pillar to post, so finally some lady gave me a settlement amount and the reference that I was supposed to use and she confirmed that that's what I owed, I paid the R2705. On the 22 December I received q text letting me know that they were going to debit R3109.79 on the 24th, I made a call to Thapelo Ncubula and still no answer, called the customer service and taken from pillar to post after answering questions, and I was told that they will request Thapelo Ncubula to call me back since am unable to get hold of him,till this day I haven't received any call, and remember I am using my airtime trying to fix this mess. That afternoon I emailed Thapelo Ncubula the proof of payment and explained what happened, his response was he was out and said I should contact Khensani Mojela,till this day I haven't been able to get hold of her too. On the 24th they debited and 3 reversed the money because that money was for other things. On the 05th January I called more than 3 times and still was not assisted, like before I was asked questions, had to explain my story and taken from pillar to post and still not assisted. Was given numbers to Charlotte who is Thapelo and khensani's manager, they said she was on a call I tried every hour to get hold of her and all the time it sounded like the phone was engaged. I was told that I will not get the lockbook/ nattis(not sure of the spelling) because I owe some money and only the above mentioned people will tell me. I paid what the nedbank person told me, it is not my fault that the lady who told me the amount was not supposed to tell me, I don't work at nedbank and I don't know how they work however the person who gave me the amount knows what to do. I will not be paying any more money to the account