Demand that future payments be by certified check

A review of your account indicates that you have
had three checks returned unpaid from your bank.
While we regret having to take this action, we must
insist that all future payments on your loan be made
with certified funds. Any payment, which is not certified,
will not be accepted and will be returned to you, possibly
causing you to incur a late charge.

In making all future payments, please send them to the
attention of [name of person or department] for proper
credit.

Your cooperation is appreciated.