Wrong contract MTN

I app**** for a simcard contract which consist of data, in early March 2020,the Sim was delivered late April after that the Sim was not working but still got statements and immediately when I discovered that Sim was actually for airtime I reported it and for no response from anyone in the Mtn departments, prior to that I decided to pay the outstanding amount that was billed so that I can continue using the simcard, to my surprise it was barred then paid again still the sim was not working, went to an MTN shop at Carnival mall and they told me is was okay to use after paying about R400, since then I decided not to pay for something that is no use to me and have been sending endless emails with no luck until a consultant called me and said the Sim was not ricad but they kept on adding to the account, I'm not going to pay it and this is messing with my credit, please help what to do next.