Phone scams involve fraud/"theft" of monies, especially from the elderly. The United States Attorney Office is responsible for
criminal investigations occurring over state lines. They are a federal office and come under the jurisdiction of the DOJ.
You forgot a few things:
1) The caller must be positively identified, in order for investigations to be fruitful.
2) Many scammers use throwaway cell phones, or are overseas.
3) "Simple" DNC violations are NOT under DOJ's purview!
4) The ICCC and FTC have responsibility for enforcement of such violations.
However, the DOJ DOES pursue several "mass marketing" scams that may use the telephone for communications, coordinating their activities with other Federal investigative and regulatory agencies. They also participate in several US and International anti-scam working groups.
If you want detailed information on their progress, I suggest you ask the DOJ ... but do not expect them to publish their monthly updates in this forum.