The fast way is to change your number and to make sure it is unpublished. This is different from unlisted as it prevents the phone company from selling your number or in anyway giving it out to anyone, for any reason. Unfortunatly most phone co's charge for this, but IMO it's worth the cost for peace and quiet. My phone hardly rings, even for telemarketers.
If you want to keep your number, then you need to do it the hard way, I'm sorry to say. You'll need to get the name and address of the company(s) that is/are calling you and then send them the following letter by certified mail, return receipt (you must send it this way as proof they received it, othewise they'll just claim they never did).
If the people that are calling you refuse to give you the name of the company and/or their address (they are legally required to but often don't) you can google the number on your caller id and/or the name of the company, if you have it. You should be able to get the address that way.
After you send the letter they are allowed to contact you one more time, to let you know they got the letter from you and that they won't bother you again. If they contat you for any other reason, you can sue them for $1500 per phone call/letter you receive.
Another avenue is contacting your state attorny general's office. Many state AG's are starting to go after debt collectors for violating consumer rights. Even people who really do owe money are complaining about violations of the laws, and AG's are starting to act on it.
