So the way that phone scams tend to work is the following:

• they spoof (disguise themselves) as a legitimate NH number when they call any phone number with a 603 area code
• they'll usually call a hundred numbers at a time to see if they get a response. They usually only have about 10 callers working the phones during this time, since not all 100 phonecalls will be picked up
• they'll also usually call a few hundred numbers in bulk, record the brief response of whoever answers (when you say "hello?"), hang up, and save those audio clips to be evaluated later (checking the age, gender, etc. of the person who answered, or if the location is a business, school, etc.)

So what's happening is the following: either your voice response is being saved for evaluation to see if you're easily susceptible to be scammed, or when they call a bulk amount of phone numbers, there isn't an available person to take your call, so they drop it.

They're likely not even based in NH, they're usually based in a country where they can do this under the radar and not have harsh penalties if caught. There's really not much we can do to stop it. Don't report the NH number who called you because it likely belongs to a real person.