Get on the Do Not Call Registry. This registry, which is for United States residents, lists telephone numbers and the owners of those numbers that refuse to receive unsolicited calls by telemarketers. Register your telephone number by calling (888) 382-1222 or online at www.donotcall.gov.[1]
This list was set up by the Federal Trade Commission in 2003 and can reduce the amount of unwanted telemarketing calls by approximately 80 percent.
Some types of organizations are not under obligation to pay attention to the Do Not Call Registry. They include:

Call your phone company and request to speak with the “annoyance department.” This specialized department can place a trap on your line that inhibits specific callers from contacting you.
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Put your phone number on specific company do-not-call lists. If you’re routinely getting calls from the same annoying companies, you can tell the telemarketers to remove your name and number from their calling list. The Federal Communications Commission (FCC) requires that your number be removed from the requested company lists for 5 years.
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Use a search engine to find out who’s calling. If you’re not sure of the source of a certain number that pops up, do a search to find out. Entering an unknown number in a search engine may give you some hints about its owner. Many online report services also allow you to report and share your experience with other users.