[DATE, ex. Monday, March 31, 2008]

[NAME, COMPANY AND ADDRESS, ex.
Link Building
XYZ Inc.
1234 First Street
Suite 567
Anycity, Anystate  85245]

Dear [NAME, ex. Link Building],

A check of our records has revealed that we have made an incorrect payment to you in settlement of your invoice #[INVOICE NUMBER].  Our check #[CHECK NUMBER] for $[AMOUNT] is $[AMOUNT] in overpayment of the total amount due, $[AMOUNT].

[MENTION HOW YOU REQUEST THE OVERPAYMENT TO BE HANDLED, ex. As the overpayment is not insignificant, I would greatly appreciate the difference of $1,000 to be sent to us.]  I thank you for your consideration and look forward to continued business together.

Sincerely,

[YOUR NAME, ex. Jill Jones]