First, tell them that you are aware of your rights under the Fair Debt Collection act and that you have a copy of the FTC's consumer guidelines in front of you. (print it and place it near your phone.) Quote from it.
For example:
May a debt collector contact anyone else about your debt?
If you have an attorney, the debt collector must contact the attorney, rather than you. If you do not have an attorney, a collector may contact other people, but only to find out where you live, what your phone number is, and where you work. Collectors usually are prohibited from contacting such third parties more than once. In most cases, the collector may not tell anyone other than you and your attorney that you owe money.
What types of debt collection practices are prohibited?
Harassment. Debt collectors may not harass, oppress, or abuse you or any third parties they contact.
Example:;
* or repeatedly use the telephone to annoy someone.
more at this FTC consumer page
http://www.ftc.gov/bcp/conline/pubs/credit/fdc.htmI have used this technique to get rid of collection agencies after repeated notifications that my phone number was not associated with the name mentioned.