Cancelled line 2 years ago - account in arrears no resolution

I have been Trying to resolve a closed account for 2 years - I cancelled my account in January 2020 and was paid in full. It was a Fixed Line and DSL account Account number *** - a few months later I was contacted by a company called Nu Debt who told me my account was in arrears and I owed in excess of R2000. I went in to the Local Telkom as soon as I could and they informed me that they someone had cancelled the DSL and Internet but not the Fixed Line. I then contacted Call Center who informed me that they could see the error and that it would be resolved. I received a message a few days later saying Case no ***0 had been resolved. I now have a new Debt Collection company called DCFourie sending messages to say I owe R3463,43. I have sent multiple correspondence to the previous company Nudebt to resolve the issue. When I call DCFourie they inform me that it is due to a contract I had with Telkom...I have never had a contract with Telkom... At one point Telkom acknowledged the error that they had cancelled the DSL and Internet but not the Fixed Line- which was a bundled package