If you absolutely have to answer these calls, a couple of suggestions. Get a police whistle and let them have an ear full. Second, answer the phone with " Hello, you've reached the office of Internal Investigations, please hold for the next available agent" or something similar to that. If you're really bored, go along with them giving stupid answers, tell them to hold while you get the info they want, come back with your police whistle and use it!
When my husband is bored he will engage them, speaking like a California surfer dude...laid back, not a care in the world. He has also answered and acted like the pool boy who got interrupted while being intimate with the wife. I usually answer and blast Metallica until they hang up and then block. The police whistle is definitely a good one! ROFL