I picked multiple times. They'll say something stupid, like, "Is Marco there?" If you say "No," they'll say "Maybe you can help me." At that point, they're trying to sell you something. I always pick up so I can tell them to stop.
You should NEVER pick up - just look up "can you hear me" scams. Jeez, they've been slamming since the 80s, picking up the phone just assures the scammer of a _sellable_ live line, the fact that your line is live and active is worth something to other scammers. Data mining is legal and profitable, YOU are the resource being mined...