This is a letter you can use to demand that collection agencies leave you alone:
Request for discontinuation of contact per the Fair Debt Collection Practices Act
Name of Creditor
City, ST Zip
Dear Sir or Madame:
I have been contacted by your company about a debt you allege I owe. I am instructing you not to contact me any further in connection with this debt. Under the Fair Debt Collection Practices Act, a federal law, you may not contact me further once I have notified you not to do so.
[if applicable] In particular, I am directing you to discontinue all telephone calls to my workplace as continued calls to my employment could jeopardize my job.
[if applicable] I am hereby advising you that continued contact by your office will cause severe and permanent harm to me. I suffer from a number of medical problems and my treating doctors have advised me to avoid stressful situations such as those brought about by phone calls from your employees.
Thank you for your immediate attention to this matter.