Irritating calls from DSTV about their promotions

I am receiving relentless and ongoing calls on my phone from the DSTV call centres, trying to persuade me with their promotional garbage. (I dont know if these are spam/***** in nature, but nevertheless)

Each time I have to stress that I am NOT INTERESTED in their promotions, and that they must please not call me again. I always end with....."I will call you, not the other way around"

But the calls keep coming.

What an unprofessional organisation. This is blatant invasion of privacy. Disgusting.