Why are so many random companies calling us constantly?

Like, 3 times a day, this place... well on the caller ID it says, "2", calls us. On the message it gives, it says something about getting a lowered rate on something, I forget. Right now we just got a call from National Geographic. I didn't even know they called people. This isn't fake. A bunch of 800 and 866 area code numbers are calling us. What do I do?