Handed over for payment without notice

I cancelled my contract, got confirmation that I do not have any outstanding fees and then months later, without any communication from Supersonic I get an SMS from a debt collections company stating that I have been handed over. I asked for proof from Supersonic for proof of communication that they have informed me of this outstanding fee but nobody is able to supply this! When asking to escalate the matter I'm told that I have to refer to the debt collector. The agent in accounts department (Regan) reluctantly told me that the head of the accounts department is Heather but cannot share any work contact details as this against the POPI act.