Blocking a contact
To block a contact in Android, navigate to Settings >> Block numbers >> Add number to block list where you can type a number or choose the contact from your contacts.
Similarly, you can also block a contact from the call-log screen by choosing the '⋮' option (to the right corner of the phone number) and then choose the "Block" option.
A contact can be added to block list from the messaging tab by opening the message thread >> tap on the circle icon for blocking.
After blocking that contact, you’ll be able to unblock the contact in the same way. Navigate to "Block numbers" from Settings. All the blocked numbers will be displayed under "My blocked numbers" section. Now, tap on the blocked number >> Remove.
Note: when blocking a contact or number, in most cases the person will be automatically directed to your voicemail, without knowing they were blocked.