How do I block unwanted texts that come from a Secondary Number app?

Someone is using a Secondary Phone Number app that is available from the App Store as well as websites online. They allow a user to text me repeatedly with a different number each time. I block them as I receive them, but it is no use. The app allows for unlimited numbers. The numbers begin with a 747 area code. I have tried the TextKiller app and it does not work to block these numbers.

Apps: Text Me, Second Phone Number, SmartLine Secondary Number, TextFree, etc.

Websites: Text Me, Go Text, Text Free, etc...

HELP ME!