No Caller ID. No message from caller. I assume the caller is a telemarketer because (s)he did not identify himself or herself. Legitimate businesses identify themselves via Caller ID and via a voicemail message.
I block numbers that make unsolicited phone calls for unsolicited business.
A robo-call recorded message about lowering your electric bill. I do not answer calls with "unavailable" which most likely means it is a spoofed number. The caller wants you to pick up and press a number, which acknowledges that you are a live person. What happens with these scammers, even if you press the number to "be taken off their list" they simply call back from a different number, once they know you will pick up. Don't answer unknown or "unavailable", "Name Not Known", "Private Caller".