您可以这样说: "The payment for the new order will be deducted from the remaining balance of the previous order." 或者 "The new order's payment will be offset by the balance remaining from the previous order."
想说明新订单的货款从上次的余款中扣除-你就说上次的余款作为此次订单的订金好了.
We will treat your overpayment from the last order as the deposit for the current one.Please kindly see the attachment for
the PI in this purpose.