Use this sequence of questions and stop any telemarketer in their tracks:

“May I have your company’s name, address and telephone number? If you are calling on behalf of a client, may I have the name, address and telephone number of your company, as well as the name, address and telephone number of the company that you are calling on behalf of?”

“Put me on your “Do Not Call List”. You are hereby ordered to share my “Do Not Call Request” with your affiliates, associates, and related entities. If you are a third-party service bureau (telemarketing company), put me on your company’s “Do Not Call List” as well as your client’s “Do Not Call List”.”
“Send me a copy of your “Do Not Call Policy”. If you are a third party telemarketing service bureau, send me your company’s “Do Not Call Policy” as well as your client’s “Do Not Call Policy”.”

“If you call me again, I will use your product or service and not pay for it. My denial of payment will be based on the fact that your future calls are a violation of an act of Congress, and any contract that is entered into as a direct result of an illegal act is unenforceable.”

“Do you understand what I have just told you?”

“Will you comply with my requests?”
—Hard-core Telemarketing Opt-out Script.