Dear <debtor name>:

We are interested in our customers and are always trying to find new ways to improve our service. For these reasons, we are inquiring if there is a reason for your delay in paying your long overdue account. If we can help – by making your payments smaller or extending our terms or by recommending a loan company – please let us know.
We would appreciate a word from you – as well as your check.

Sincerely,
<your name>
<title>