I got the call, hung up all I got when I called back was that the number was busy.

Received a call from 1-800-861-9373 but wasn't able to answer. I wanted to know who was calling me because I don't like answering a call without a caller ID.

called, hung up on me, and I have never signed up for a medical seminar.

This number called me and left a message. It was for a free medical seminar that I had signed up for.  It was just a reminder for the seminar.