This is what I do:
When they call, in the most serious robotic voice you must say : this call is being traced and monitored to ensure my safety.
Right away their palms will start sweating, and their headset will become suddenly uncomfortable resting on their head.
Then, you must laugh like a hyena. A demonic, possessed, hyena. This will enlist shock and surprise, and to really seal the deal you must put your phone on speakerphone and begin beating on your chest like a gorilla. This will let the caller know you are the dominant male in this "strictly business" relationship.
Now here's when things start to pop off. Avoid using statements like "your mom got it for me" or "that's what she said" but at the same time you have to convince the caller that you are clinically insane and that you're going to murder his entire family. You're fed up with the calls, you performed a military grade backtrack to get his location, and you're coming for him.
Former telemarketer (lost my wife, kids, and pet cactus due to a similar scenario)