@dega2010- Your friend told you correctly. There is a law that was passed by Congress called the Fair Debt Collection Practices Act. This law protects the rights of debtors. In a nutshell, if you tell a creditor to stop calling you, they have to stop.
The next time they call, tell them that you would like for them to stop calling you at home and at work. After your conversation, send them a certified letter saying the same thing. According to the Fair Debt Collection Practices Act, they can still call you if you do not submit a request in writing.
If they continue to call, let them know that you are aware of the law. Tell them that you will file a complaint with the FTC if it continues.