The Direct Marketing Association of South Africa (DMASA) is a Section 21 Company and self-regulatory organization empowered by law to ensure that direct marketers adhere to a strict code of practice, and to protect the rights of consumers when buying from direct marketing organisations.
The DMA's website carries a national opt-out database where, once registered, you will not be contacted by any member companies of the DMA.
References
Direct Marketing Association (South Africa) Wikipedia(Text) CC BY-SA