These people usually call from premium numbers, depending on your phone some will allow you to block these numbers in your settings, or download a call blocking app and set it to block all premium numbers.
My current phone has built in call blocking and I've set it so that only my contacts get through. With previous phones, I used a third party app. There lots of free ones, but they all have limitations and some work better than others.
The fault, dear Brutus, is not in our stars but in ourselves.