Most companies sell mailing lists. Since there are so many companies involved, it is hard to say where the information came from. This is why you should always opt out of the "advertising partner" stuff in your privacy preferences. The bigger question is why, industry wide, these lists are opt-out instead of opt-in.
It's got nothing to do with knowing you're a Dish subscriber. They're somehow getting enough information on subscribers to get the channels turned on while they're on the phone trying to get the subscribers to pay. Sounds like a serious information leak to me.
Dish is sending out emails to all their customers regarding this.