Called and left no message.

what a nuisance, keep calling but no message

Calls and leaves no message.

Calls and never leaves a message.  Caller id says Unavailable, well, so am I!

It is a robocall. If you don't answer, it stops ringing by the time your voice mail or answering machine would start. Robocalls usually only hang ong for 3-4 rings and then drop. Now this doesn't mean they won't call back.