If you can get S7 link with Telco, in most cases it's trivial to spoof Caller ID signals, as those are essentially forwarded from originating network. Getting direct S7 link isn't as hard as it sounds, it's IIRC common thing if yo want to run VOIP provider.

Your telco's NOC can at best track what "port of entry" the call came from but can't force the Caller ID go be truthful.