Here’s where to get the app:

After install and open the ActiveArmor App:

ActiveArmor Home Screen, Tap the Calls Icon
Call Page Tap on Blocked icon
Make sure our number 5036837202, 9027019367 and 5037446210 to unblock
if you found it blocked, tap on the number to Unblock it

More detail on ActiveArmor https://www.att.com/support/article/wireless/KM1252907/