Dear Felix
I am in receipt of your invoice #[INVOICE NUMBER], dated [DATE, ex. June 8, 1998].
[STATE WHAT YOU HAVE AND HAVE NOT RECEIVED, ex. Although the shipment of 20 compressors has arrived, we have not yet received the 2 1/2" piping required to install them.] I will be pleased to send you a check in the amount of $[AMOUNT] once we receive the above item {s} and the order is complete.
Regards
Lydia