calls at least twice a week maybe more ...leaves no message

I've received calls from this number but nobody ever says anything.  I've had several calls from this number so since they won't say anything I won't either.  They will usually hang on for about a minute.  I've blocked it several times as well and for some odd reason it keeps popping up.  :)

Called me & i called back & it's a automatic voice sayin "hello are you there.

Auto message that said: "Hello this is Joe, an unemployment specialist, and I see you were on one of our job sites recently, can you hear me ok?"
I hung up once I heard that.