[Your letterhead, if desired; if not, your return address]
[Date of letter-month, day, and year]
[Recipient's first and last names]
[Street or P.O. box address]
[City, State ZIP code]
Dear [recipient's name]:
I’m writing to follow up with you about invoice number 1114 for $475. Payment for this invoice was due to me on 11/25/10, but I have not received this payment yet. Please reply as soon as possible, or call me at 444-1797, to inform me of the status of this payment.
Thank you for your prompt attention to this matter. I look forward to hearing from you.
[Sender's first and last names]