456, X Street, Y Avenue,
[Subject: Normally bold, summarizes the intention of the letter] -Optional-
Dear Jack Martinez,
We would like to confirm that we received your payment of $67 through your account. We would, however, like to inform you that the total charge that was listed on the invoice we sent you was for $80. We hope that you could correct this by sending us the remaining amount.
If, however, you feel that this is an error that occurred through processing or may be an issue on our end, don’t hesitate to give us a call at 333-3333 so that we can get to the bottom of this and fix this situation as soon as possible. Thank you for your time.