Borderline harrassment and destroying the clients brand

I was called an asked to participate in a "short survey" after 15mins of detailed questions and being told "its almost over" i gave up and told the agent we were done and I did not want to continue. Since then he has called me 6 simes in less than 24 hours. I have told him more than twice that I no longer want to participate and that he is now harrassing me. The trouble is that it not only tarnishes the brand of Ask Africa, it also tarnishes the name of the organisation they represent, who i know well and is a client of mine. Should this continue I will take this up and provide feedback to the client about the manner in which the supplier is representing their brand in the marketplace. It's completely unacceptable and unnecessary. If you say it's a short survey, be short.