Caller ID said 'NOT IN USE'. I almost laughed. Someone chose that one. So, since it is not in use, I picked up, but said nothing, and was responded to in the same way. After about 20 seconds I just hung up.
Actually, that is not a good idea-if you answer (or press 2 to get off their list) they know that the number is "alive" and will forward the information to other companies/spammers. As a result, more calls will be received by victim.
Robocall from an energy company. I started pushing buttons to avoid listening to the message and get to an operator. The person said "I understand that you are interested in changing your energy provider" to which I replied "No, I want to be removed from your calling list"
He said "I'll see what I can do to help you" and hung up on me.