A legal firm harassing the wrong person for an outstanding debt

For the past year, I have been harassed with emails from a debt collection company. Each email gets more and more aggressive as they try to intimidate the recipient to pay their outstanding account. I have responded to the emails multiple times to tell them that I am NOT the person that they are looking for. I have called the company multiple times to tell them that I am NOT the person they are looking for. Each time I call they ask me for my ID Number because they need to look up the account. I tell them that the account is not on MY ID number because it is for SOMEONE ELSE. Then they say "Sorry, we can't help you." I have subsequently informed them that if they do not stop the harassment, I will expose the fact that they are disclosing someone else's personal information (the person with the outstanding account) to a third party (me) that is of reputational damaging nature (I now know that this person is in trouble for an unpaid amount). This must be against the POPIA Act. How can a Legal company, Munnik Basson Dagama, not take this seriously?! What if the person who should be receiving these emails is unaware of the outstanding amount and could have settled it ages ago? Must he/she now be blacklisted because the company keeps sending their demands to the WRONG PERSON? And why, oh why do they not listen when I've told them via email and telephone that they are making a huge mistake here?