Steps for iPhone Users
On the Home Screen, select Settings.
Within settings select Messages.
Under SMS/MMS, select Blocked
Select Edit in top right corner
Select the (-) sign beside the 5 Digit verification number on the blocked list and choose unblocked.
Steps for Android Users
On the Home Screen, select the Phone icon.
Tap Menu (this is the 3 vertical dots on the upper right hand of your screen)
Select Block Numbers. You will be able to see all the blocked numbers on the screen.
Select the number that you wish to unblock by tapping the minus (-) sign beside it.