The DNC would not apply to the federal government agency's nor any kind of a debt collection anyway. The DNC is not a call blocker and does not protect you from from the illegal callers, extortion scammers, foreign country's and frauds. Criminals do not obey laws simply said. They use spoofed numbers which make it hard to track them down.. it takes time to do this and many subpoenas for call records.
I came home to an automated message on my voicemail. Needless to say, I did call the number and a person answered "hello" I said someone left me a very serious and scary message from this number. then she replied "IRS. Hold on" .She hung up and when I tried it again several times later, the line was busy. As a law abiding and tax paying American, I was and am really upset about this.