Simply replace the unfilled areas such as "" and "[date]" with your information.
Enclosed please find a copy of your statement showing a past due balance of [total due]. This balance dates back to [oldest date owed] and is now seriously delinquent.
Please understand that we are willing to work with you if you cannot pay the entire amount due at this time. Please contact our offices immediately to make payment arrangements or set up a payment plan.
If we do not hear from you within fifteen days from the date of this letter, we will assume that you are not going to pay this bill, and we will take appropriate action, up to and including sending this balance into collections.