Unjustified judgment

Had a 20GB LTE contract with Telkom. Was coming to an end in Feb 2018. So on 9 Jan I sent through a cancelation form. With numerous follow ups the account was only closed in June/July 2018. Asked for a query to be raised on the amount they said I owed a few times with no result or even feedback. I eventually figured that it was resolved because I didn't receive any statements following that. Long story short. I get a call from a company called Debt in over a month ago calling on behalf of telkom and find out I have a judgment against my name which directly affects and is currently affecting my job as I'm in the financial industry. I had to just make an arrangement to pay debt in every month cos I have no other solution as Telkom will not look into the issue. Im paying money I don't even owe.