To block unwanted callers using an Android device version 4.4 KitKat or later, open the Contacts application, select Settings, go to Call, tap Call Rejection, and then select Auto Reject List. On the new page, click Create, insert the phone number of the person you want to block, and then click OK or the tick icon at the top-right corner of the page.
Alternatively, open the Contacts application on your Android device, tap the contact name you want to block, and then tap the Menu button. On the shortcut menu, click Add To Reject List. A block sign appears next to the contact when you enable call-blocking mode for the selected contact. For Android version 4.2.2, create a contact out of the incoming call, click the People widget to view the new contact, tap the Menu button, and then tap All Calls To Voicemail to divert all calls from the selected contact to voicemail.
You can also download and install Android applications such as Mr. Number and Call Control to block unwanted calls. On the two applications, submit a list of contacts you want to block from calling you. Mr. Number lets you block incoming calls and texts from specific area codes or numbers, including private or unknown numbers.