Write a letter complaining against disputed billing error.

Dear Sir/Madam,

I am writing this letter to dispute a billing error on invoice No. _______ you sent to me on (date) in the amount of (----------) for mini 2WD upgrade parts.
According to your invoice I ordered two quantities of Large Diameter Aero Wheels (item no. ____). However, this is inaccurate because I only ordered and received one quantity of these wheels, delivered to me on (date) via Parcel Post. I am requesting that this error be corrected, and that I receive an accurate invoice statement.

Kindly investigate this matter and correct the billing error as soon as possible. You may contact me at the above address or by email (________ ) if you have any questions regarding this matter.

Sincerely,