Shows up on caller ID - Do Not Display - rings 3 times and quits - 4 calls from this number today -

Keeps calling and won't leave message. I put them on my phone's blocked call list.

calls and does not leave a message. Scammer

Called my work.  Answered, waited 2 seconds & hung up.

Dale got "do not display" on caller ID.  I got "unknown name".  No real difference.

Their robo-caller stayed on the line, just long enough to leave a 3-second-long dial tone, and hung up.

unknown name - do not display.  Either these people are afraid that you won't pick up if they give their real name, or they have no respect for the people they are calling.