When you receive a request for payment, you must respond to it as soon
as possible. Before you write a letter, you must have all the information about
the problem. Your reply letter should explain the situation.
If you ask for extension of credit, you should apologize for not having cleared the account on the due date, give reasons why you have not paid, and when and how you will clear the balance. Moreover, remember that this type of correspondence should be handled by letter, not email or fax.