Dear

We feel that there must be a reason why you haven`t answered
any of our inquiries about your overdue account in the amount
of $

If there is a problem regarding the enclosed bill, won’t you
please telephone me at the above number, so that we can
discuss the situation. Whatever the source of the problem is,
we are in the dark until we hear from you.

If this has been an oversight, please use the enclosed envelope
to mail us a check for the full amount today.

Thank you for your anticipated cooperation in the prompt
handling of this matter.