Called here twice in last two days.  Did not leave a message.Scammer or telemarketer

I have gotten quite a few of these calls.   They would call and not leave a message or when I answered they would hang up.  I called the number and it is Eco Energy.  I asked to be removed from their call list.

Received call and went to voicemail with no message being left. I called back and only music played with nobody answering the line??