There has been an increase in robo calls lately, and depending on where you are they can also spoof the numbers to make it look like these are local numbers. There is a robo call blocker if I remember correctly, although I'm not sure if it is a paid service. However, if it's not a robo call then I wouldn't know what to do as well. I don't answer calls from people I don't know unless there is a text message beforehand, but I suppose getting many calls in one day would be annoying even if left alone to ring.