Unauthorized billing

I received calls dec 2018 consultants of jet harassing me with free airtime and data saying they promoting new system of free WiFi or something of sort. I kept telling all this consultants I don’t want the data or the airtime because I know the next thing it will be billed and I have closed the account. Now I’m shocked that since beginning of 2019 I owe edcon and I have been in contact with them to tell them I did not authorize this and I asked for recordings as well but every time they promise to sort it out but never. I never even get ref number for my calls and not even email confirming what I have enquirer about . I now receive risk letter in my name . So edcon has ruined my credit for nothing. I hate edcon they have very bad customer service when you complain they don’t solve your problem or even bother to send acknowledgement email . I’m now taking matter to ombudsman