I talk to them. I pretend I'm interested. I ask them to hang on, then set the phone down and come back...whenever. I had a guy ask what I use internet for, and I just replied (with heavy breathing) "****." He hung up immediately. If they're a female, I buy into it for awhile, and then I start breathing heavy in the phone and asking....questions.
I give them fake addresses. I act dumb(er). I don't hold back and use choice language. I waste their time as much as possible. I try to drag it out.
I've researched them and I've called them back. I have been in the car and they called with a robot that said, 'call for more info', so I literally called the same office dozens of time, each time, asking for a new name, wasting their time until they blocked my number. One of the guys in the office called me a loser for calling repeatedly and wasting their time, and when I asked how that was different than what he did all day long, he conceded "Fair point".
They WILL take you off the list. I don't get many spam calls lately. If it's a legit business, I just tell them, if you call me again, I will make it a point to never do business with them ever again. Here's looking at you, Wyndham Hotels.