1234, Main Street
Boston, MA 02123
04 April, 2005
<Recipient Address Goes Here>
Re: Account No. <account number>
This is to inform you that your above-mentioned account with us is now [no. of days] days past due.
In the past, we requested you so many times for the payment, but we did not hear anything from you. We have not received payment since the last three months from your side.
Now, we are warning you that if we do not hear from you or receive a payment in the amount of [$ ??] within [no. of days] from this notice, then we will have no other choice, but to hand over your account to a collection agency.
So, we advice that if you want to keep your good credit rating and, avoid dealing with a collection agency, then please contact us today or mail your payment as soon as possible.
Thank you for your prompt attention in this mater.
encl: <List of enclosed items goes here>