Which of the Following Is the Most Effective Statement in a Letter

Which of the following is the most effective statement in a letter to a customer about an order for which the customer has not yet paid?

A) We cannot ship your order until we receive your payment.
B) Your order will be cancelled unless we receive your payment right away.
C) As soon as we receive your payment, we'll ship your order.
D) Your order has been cancelled because we have received no payment.