To manually add a number to your block list, select the Manage icon and select the Block tab. 

Select the + button located at the top right-hand corner and manually enter the 10-digit number you would like to block in the search box. Recent activity will appear as you type, selecting any number in the results will show a check mark over the icon, you may then select the “Block numbers” button at the bottom of the screen to add one or multiple numbers that you may have selected. 

If the page displays "No recent activity found. To block this number, tap search and select it", follow those steps, and then press “Block numbers” to add the number to the block list.

If the number is listed on your Activity screen, select the number and from the expanded view, select the “Block” icon. You may also select “More” and “See details” to view options to block the number.