Cell phones have made it much easier than before to know who is calling you. However, you do not want unwanted callers constantly calling you. So, you can block numbers. There are several ways to do this. Sometimes, certain cell phones allow you to block phone numbers in your contact list. There is a button for that. The Android phones has you use the call logs tab to block the number. You will then go through a series of steps to get to the call settings before blocking a phone number.
If none of these works, then you can call or go onto the website devoted to blocking numbers. It is the Do not call registry site. You can put your own phone number in there and then enter the phone number you want blocked.