Dear (Name of Customer Service Representative):
I would like to call to your attention a service discrepancy.
On (date), I ordered a (Type of product) from your company. I also (enclosed a check/charged my credit card account) for (amount). It was my understanding that I would receive the (Type of product) within (length of time).
It is now (date), and I have not received the (Type of product). But my records show that you (cancelled my check/charged my account) on (date), and I have enclosed a copy...