Bad service from Zolile a supervisor at Vodacom

I am so disappointed by Vodacom, I have been having difficulties with paying them because I have a contract with them then last year they told me they will not give me airtime anymore then my installment will not go up so that I can pay it off. I owed them plus minus R5800 all of a sudden on the 1st of October last year they loaded airtime I was shocked but I didn't pay attention to it, so on the 15th December I paid them R2000 knowing that in January 2019 I'll pay R2000 again nd owe them plus minus R1800, however due to the fact that they've been loading airtime my balance went up. So I decided to call them and they told me I now owe them plus minus R6000, so I was shocked cause I was under the impression that I owe them plus minus R3800. So when I called them told me that because they've been loading airtime I now owe them a lot so I then asked to speak to their supervisor then they put me through to him and his name is Zolile. I then spoke to him and asked why is that they keep giving airtime while they know I owe them cause with my knowledge according to the NCA law you can't give credit to someone who is not able to their initial credit I then told him that they are over indenting me cause they can see I've been struggling to pay them. He then said to me and I quote "what ever law you are talking about I am not aware of that so there's nothing we can do". The supervisor was so rude I even told him that I will hang up and I definitely going to take this matter further, he didn't even care or try to make me understand as a customer or do something to make both parties happy meaning me and them as a business cause he said "it's fine you can hang up". So I am really disappointed with Vodacom and their employee I would like something to be done about this matter.