I received an email stating I had purchased a $100 gift card which I did not.

If the only evidence of this charge is an email make certain the email is actually from Apple. Read here for how to identify legitimate Apple Emails: Identify legitimate emails from the App Store or iTunes Store - Apple Support

You can log in to https://reportaproblem.aplpe.com to verify any and all charges made on your account within the last 90 days and raise an issue with them as well as request a refund.

Also read here: Avoid phishing emails, fake 'virus' alerts, phony support calls, and other scams - Apple Support

Follow the steps here to access your entire purchase history: If you see 'itunes.com/bill' or an unfamiliar charge on your statement - Apple Support