I used to get these calls a lot, unlisted number. Often the phone would ring and it would be silent when you picked it up, then after a few clicks someone would come on the line. I got really sick of it and started to hang up on the silence. They got me on a bad day and I told them that there were young children in the house and that the silent calls were terrifying them and that if I got another one I would call the police. Never got another marketing call.