A Letter to Foster a Healthy Business Relationship and a Reminder of Payments

Hello, I want someone to write me up a letter with the instructions below, should be at least 200 words:

XYZ Company has threatened to cancel their marketing services with us. We are bringing in business for them, but they are not convinced our methods are working even though the early results have been strong. In addition, they have not paid their last two invoices and their credit card on file has failed. Please write a 2-3 paragraph letter addressed to their CFO that discusses why it is beneficial for them to stick around, and notify of the outstanding balance. The intent of this email is to foster a healthy business relationship.