Someone is using my Apple ID?

That is a spam/phishing email. No one has used your Apple ID to buy anything and DON"T click on anything in that message. Apple does know how to spell the word "cancel" correctly. Plus the will address you buy the name you have on file, not your email address.

Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support

Change the password for your Apple ID immediately. Report the issue to whatever credit card they are using to pay for things.

Please explain what you mean by they are using your Apple ID to buy things.