Simply hang up instead of thinking of ways to mess with people who are required to read from that stupid script and probably hate their job?
This is precisely why I like to think of ways to make them laugh or weird them out at most, rather than frustrate or humiliate them. I've never actually done any of these, but here are a couple I've thought of doing:
1. Pretend you're from a different time period or a fantasy world or something. I once had a daydream about doing this where I was a faery tale princess. I would open with "Hello, if you'd kindly send a letter with your request to the Royal Postman and tell them Princess Millicent sent you, I'd be much obliged." I'd then pretend to be said postman, and, after joking about having never heard of the contraption of which they speak, telling them that they may have inquired about a vision the princess has seen in the magic mirror, but that the caller must hurry in providing a solution before the princess falls victim to the evil sorcerer's curse. In the daydream, the caller laughed and hung up, needless to say.
2. If you know a foreign language, speak entirely in that language and try to convince the caller that you don't know any English. Although be sure it's a language they probably don't know--i.e. if the caller sounds Indian, don't speak Hindi or Punjabi. French and Spanish are probably not good ideas no matter who the caller is, since those languages are pretty commonly known.
3. Make baby sounds the entire time, and try to eat the phone as well.
4. Act like a famous fictional character, if you can do a good impression of one. I once had a daydream about this where I pretended to be a Pikachu.