Simply replace the unfilled areas such as "" and "[date]" with your information.
Dear [Collection Agency],
Re: Account [number] with [Original Creditor] in the Amount of [$ amount]
This letter will serve as legal notice under the provisions of the federal Fair Debt Collection Practices Act, to cease any and all communication with me regarding the debt for the account number referenced above. Should you fail to follow this notice, I will file a formal complaint against you with the Federal Trade Commission and the State's Attorney General Office.
I have chosen not to work with a collection agency under any circumstances. I will be working directly with the original creditor, [Creditor], to resolve this matter.
This letter will also serve as your notice that should any adverse information be placed against me within my credit report, as a result of this notice, I will take the appropriate legal actions.