keeps calling my house but leaves no message, hangs up when my answering machine comes on.

It is coming up unknown caller. It calls about 5-10 times a day.

Tonight they called my cell phone, which I don't often give out.  They know my full name, so it was not a robo call.  I asked how they got my number.  Said they were doing a survey (political?) and could not reveal who their client was. He was polite.  I told him I do not give that number out frequently, and that it is not for distribution.  I asked him to please ask his client to remove my number from their list, wished him a good day, and said Good-Bye.

Got a call from this number, they didn't leave a message or anything.

Why do I keep getting calls from this unknown number? Never leaves a message.