Dear

Perhaps you have overlooked the fact, but your account
with us is currently overdue. I have enclosed a statement
of your account, which shows a balance due of $

If there is some reason why you have failed to remit your
payment, please call us, and let's discuss the problem.

If it would be more convenient, please feel free to write
a note at the bottom of this letter and send it to my office
in the enclosed envelope.

Thank you for your prompt attention to this matter.