Adverts disturbing contents consumption

Can some one please explain to me where does Mtn and Telkom get the permission to slot in adverts in between contents that i might be watching? I use airtime & data paid for by myself each month yet they disturb my listening or viewing with this advertisments. I am refering to this two networks since they happen to be my current service providers. I mean i would not be watching or listerning to those adverts if i did not have data or airtime recharged with my hard earned money. Its even worse for their chosen adverts to be played in the middle of News reports or an important documentary.