Remove me from your database!

I have been receiving unsolicited phone calls on my landline and cellphone for several months now from call centres attempting to sell me insurance or offer me loans. I finally managed to find that I'm listed with the Direct Marketing Association of Sa and they are handing out my number without my permission to these marketers. When I do an internet search for their contact details the number listed doesn't exist and it's impossible to e-mail them. I wish to be removed from their database and will look in to the legality of what they are doing as I have never knowingly given my consent to them to hand out my details.