Here is what I have done many times when a telemarketer calls I listen to what he wants to sell, the I say: “Yes, I think I’ll be interested in this, can you hold on just a bit?” Then I put down the phone and let him wait. Many times, the caller was still waiting 5 minutes later.
Some of them are paid/incentivized for their talk time, so the reps will be perfectly happy, in fact GLAD, to be put on endless hold, because they can mute their headset, kick back and talk to their friends while all the time their metrics look good and it looks like they're working.
Some of our reps at my old company would purposely change our AI to dial places like Medicare or social security so they could purposely get put on endless hold.