Here is a template for the "drop-dead" letter to collection agencies:
(Name of Collection Agency Or Creditor)
(Address, City, Zip)
To Whom It May Concern:
Under the federal Fair Debt Collection Practices Act, this letter serves notice that you must CEASE & DESIST further contact with me.
I have been contacted by your company about a debt you allege I owe. I do not owe the debt.
Any further contact of me regarding this debt will result in legal action.