DSTV harass me - Call centre agents are rude and unprofessional

I have been phoned numerous times by agents wanting me to upgrade to the explorer package. After informing them that I am not interested, they speak to me in a very unprofessional manner. They become rude and harass me. I have had 2 calls in the last hour alone. Not to mention calls from the weeks before. This is not acceptable. I am a client, and the manner the call center agents speak to clients is not professional at all. What will be done regarding this ?