It's the Red Cross, requesting blood donations. I did speak with someone. It's an auto dialer, which is why sometimes there's no one on the line when you pick up. It will keep auto-dialing multiple times per day/week, until you speak with a live person & they can move the next contact date.
Just received a call from this number staying that they are with the Red Cross and asking me to set up another blood donation appointment. They knew where I previously donated, but upon further investigation they provided donation dates that my center does not have available (such as Thanksgiving morning). I've only ever received legitimate calls from Red Cross from their 800 number. My advice is to NOT set up an appointment over the phone if someone from Red Cross calls you, but to either call them back at 1-800-RED-CROSS or to set up an appointment via their website (www.redcrossblood.org) or their mobile app.