How can you get back at Extended Auto Warranty companies for harassing phone calls?

If they are a telemarketer, you can ask them to stop calling. If they are a third party bill collector, you can ask them to write you instead of calling.

However, to answer your question, the best way is to take up their time. So if they are selling something, let them give their spiel. Ask them questions - a lot. But make the real questions. Verify all the info. But then buy nothing.

If it is a debt collector, let them do their spiel. Go over all payment options. Explain why you can't do any of them - but explain one at a time, to each suggestion.

Remember, in the case of both, they are to collect a debt or make a sale a certain number of times per day, and spend a certain amount of time per call. A short time, is what is wanted from their boss's perspective.

Now you know.