Ask the referee or a league official for which officiating organization the referee works. Write this name down and any other information that comes with it.
Go to website for the National Association of Sports Officials and fill out a contact order form so you can get a list of local high school basketball associations in your area. They will send you information about how to contact your league office.
Write out your complaint in an email or in a hard copy. Do this in a professional manner, citing the exact calls you disagreed with and any evidence you have to support your complaint. Send the email to the officiating organization as well as any coaches or administrators at the high school, so they are aware the complaint was made. If you are sending a hard copy, note that you are sending the letter to the organization and to school administrators or coaches. Send photocopies to all parties who you want to see the complaint, so they can keep the information on file.