There was a delay for the caller to respond to my hello, typical of a robo call.  I assume it was a recording that that said, "hello . . . hello . . . hello . . .  I am sorry but I can not hear you.  Call me back please."  But I did not call back.  A few minutes later, the same number called again.  This time it was a human telemarketer.

robo said GOODBYE

I just got the same call, robo said GOODBYE. They are just trying to tease you into calling them back, so they have your number associated with an active line.  I'm not calling back.

blocked call back;you've reached a number no longer in service.

Got this call yesterday. Did not p/u. No message left.