How can one stop continuous harassment from MBD (Munnik Basson & DaGama)?

This company calling themselves MBD have been harassing me for 3 months now after I have repeatedly informed them that I am not the person they are looking for and that the number they are dialling is not the person they are looking for. I am not sure where they purchased my number, but they refuse to delete it from their database and the caller refuses to give more info about the company that they are calling on behalf of. So I went on the internet instead to find out a bit more about them and there is heaps of info on them.

Looks like MBD refers to Munnik Basson and DaGama Inc.

What I have heard is that MBD is in the business of buying Debt books and then harassing and bullying people into paying elevated repayments. These bloodsuckers should be eliminated like we do with mosquitoes. If they want to buy debt books, then I suggest they should keep the debt book and stop trying to profit from people's hardship. People who make money this way are one of the worst form of humanity I can think of.

Since the changes in the credit act you are no longer obliged to respond to bullies like MBD.

How can one stop this continuous harassment?