Below is an example PFD (Pay for Delete) letter you can use.
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Collection Agency
1212 Maple St
City, State Zip
Re: Collection Account for Original Creditor Account #: 00000xxxx
Amount: $25.00
To Whom It May Concern:
This letter is to inform you that the validity of this debt is disputed. I am not sure of the account number, as I have never heard from you regarding this account. The account number I have is the one listed on my Experian credit report – which omits the last few digits.
In the spirit of compromise, I am willing to pay this account IN FULL (or settlement percentage) if you agree to immediate deletion of this account from any and all credit reporting agencies (Equifax, Experian and TransUnion). The purpose of this settlement is merely to have this item removed from my credit files. It is not to be construed as an acknowledgment of liability for this debt in any form.
If you agree to the terms and accept this agreement, certified funds for the settlement amount of twenty-five dollars ($25.00) will be sent to Collection Agency in exchange for full deletion of ALL references regarding this account from my credit files and full satisfaction of the debt. As certified funds will be used for payment, there shall be no waiting period regarding the deletion of this account from the credit reporting agencies.
Collection Agency agrees to delete ALL information regarding this account from the credit reporting agencies WITHIN TEN CALENDAR (10) DAYS following receipt of payment as specified above and will not discuss the terms of this settlement with anyone, excluding your client on this account. If contacted by any third party, including credit-reporting agencies, Collection Agency will not acknowledge that any settlement offer was made, accepted or executed and will, in fact, deny knowledge of any such account.
If you agree to the above terms, please prepare a letter on your company letterhead explicity agreeing to the same terms as the above settlement offer and have it signed by an authorized representative of Collection Agency. It will be implied that this letter shall constitute a legally binding contract, enforceable under the laws of my state.
Your response must be postmarked no later than 15 days from your receipt of this settlement offer or this offer will be withdrawn and I will request full validation of this alleged debt, as provided for by the Fair Debt Collection Practices Act.
Please address all correspondence regarding this account to:
You
123 Any Street
City, State Zip
Please keep in mind that a PFD is a type of good will letter. Do not use the word dispute anywhere in the letter or it can cause problems. Also, you cannot give the CA/creditor any time limits on removing the debt if they chose to do so, or tell them who they can and cannot speak to. 
