Useless, ********* and harassing

This supposed law firm (but is actually just a debt collector) keeps harassing me about a Cell C account (apparently a cancellation fee from a fibre contract that I cancelled 2 years ago. They never told me about an outstanding fee, and I never heard anything for 2 years until Hammond Pole started calling me). I have paid the outstanding balance, have sent them the proof but I still keep getting emails and sms's from them. They should be disbarred and prevented from operating a business