Called left no message

I answered gruffly to this number I didn't recognize. A woman's voice responded with a perky "Hi!" but nothing more. I asked what she wanted - no response. I hung up & blocked the number. Caller ID just showed 'St Louis MO'.

Called left no message.

so tired of this number calling and when you answer the phone and say hello all you hear is breathing in the back ground. If my answering machine pics the call up from this number there is no message left

I believe there are bot programs out there, that call people, and if any message is left it's also dead air.  I believe these computer programs run in order to figure out which numbers are likely answered by live people, and the people running them compile lists to sell to spammers.  I also believe that seedy individual people trying to make a buck are starting to do the same thing.  Call, see if they can get someone to answer, and at day's end have a whole slew of phone numbers to sell to scammers and spammers.  I have no proof of any of this.  But it would make sense.  It just doesn't do to answer the phone if you don't recognize the number.  I have done away with an answering machine on my landline.  It just wastes my time.