multiple calls daily  no idea who it is

Just had a call from this number.  I did not pick up and they did not leave a message.

Continues to call and doesn't leave a message . So most likely a spam call.

I kept receiving phone calls from this number at all hours - no message - so I decided to call and find out what the callet wanted.

It's an online university sales call.

Continual calls daily.  I was told to never answer any number beginning with 100 or 200.