This forum doesn't cover FreePBX.
Asterisk doesn't have built-in capabilities for such high level operations but it has the tools to implement them if you can specify an algorithm that unambiguously distinguishes the different cases. Will number length work?
The ITSP should fix this, as I consider it broken. I guess they are forwarding the digits received over ISDN without also forwarding the type of number (TON) code information, and that the ISDN operator is sending caller ID with different TONs, rather than sending them all in international format.
I imagine they will have problems with Skype for Business users, as that uses + format, international, numbers, for everything.
This forum is a discussion forum, not a help one. Use Asterisk Support for that. For FreePBX help, use http://community.freepbx.org/