If th person calling is like every other Indian call center employees no one can understand what they are saying anyway.
Just to them to **** off and hang up.
Next time have a loud referee whistle and tell them to turn up the volume because you can't hear them. Then blow the whistle as loud as you can!
If it's a female ask her whether she likes to suck cock.
If it's a male ask them if he likes getting fucked in the ass.
I once got pissed off with JWs coming to my door. The last time they rung the doorbell I opened the door naked with my cock in my hand.
They never returned.
Go to be 'proactive' with these chretiens.