This number has been calling my office repeatedly, sometimes multiple times in the same hour. They typically call late in the day. The caller ID says "Home Security." I have to answer the phone even if I can see it's this number, and each time there is no answer: they just hang up. Calling the number back results in an automated message inviting you to press 1 to be put on a do not call list. Needless to say, that does not work. It's probably not advisable to do it, anyway, so I wouldn't bother.
See Tamianth's post, a call blocker may be of some help, but if you don't wish to spend, do NOT take unknown calls in any way. If you are able, try turning off your ringer if you don't risk missing anything important. Calls you have questions about you can look up. You'll want to make sure these callers get NOTHING when they call, even an automatic answer. Patience and time is the key, but you can get pests tired of calling your number if they get no kind of answer from it. Numbers that have nothing are worthless to them. Since you say there's nothing said, they're likely checking on when they get a live voice and recording the times for other pests. Just make sure there's no answer of any kind when unknown numbers call and that's a step in getting them stopped.