Do not answer calls from number you do not know. If it is a good call, they will leave a message. It it is a scam and you answer you could be charged for the time you have the line open. Maybe a small amount but it may appear on your phone bill as a few cents but multiply that by thousands of call and these creeps have made some serious money just by getting our blood pressure up. Plus you have let them know that the number is a good one and they resale you number to other robos.