Paid up account still in arrears arrears after 15 months

I paid up my account in June 2019 but in August 2019 when I wanted I use the account I was told I had an outstanding balance. When I checked with their head office account department I was told there is a value added service that was loaded on my account in April 2019 at their Malelane branch. They were unable to give me the details of who signed for the service to be loaded and the date it was loaded as I was never at that branch. I tried talking to them on monthly bases until now my account is still in arrears and worse it has been handed over for collection and to the credit bureau.I went to their lydenburg branch several times for assistance but the staff couldn't help as the account has been handed over. They tried to assist by calling head office but nothing was done. I wrote emails to them about this but still nothing has been done. I can't use the account because of arrears and it affects my credit ratings negatively. Every time I talk to them they promise it will be sorted out in 7 days.