Dear :

We still haven't received your $ payment for the [item] you purchased on [date]. Since your account is [months] over due, we have to add a late charge of $ in accordance with our credit policy. The new balance is $.

Please send your payment today. If you have difficulty paying the full amount now, please call me as soon as you receive this letter so that we can arrange a payment schedule.

Yours sincerely,

[name]

[title]