123, X Street, Y Avenue
[Subject: Normally bold, summarizes the intention of the letter] -Optional-
Dear Austin Parker ,
After reviewing your account with John International, it has come to my notice that 60 days have passed since the due date.
The payment of $1,000 has not been collected, which you promised three months ago. Because of this I have had to close your account at John International.
We hope to continue doing business with you in cash until you have cleared your previous debts. I wish we have good working relations and so I wish you best of luck.