Someone used my Apple ID

Do you think your Apple ID has been compromised? See  https://support.apple.com/en-us/HT204145. What is your evidence?

Are you using two-factor authentication? If yes,

Check your Apple ID device list (https://support.apple.com/en-us/HT205064) and remove any device that shouldn't be signed in using the steps in the link.

If there are none that shouldn’t be signed in, then you should not have a problem at this point. But, if an unauthorized device signed in, Change your Apple ID password https://support.apple.com/en-us/HT201355 

Here is What to do after you change your Apple ID or password https://support.apple.com/en-us/HT204071

How do you know someone used your Apple ID? If this is an email you received, has your credit card been charged? Are you sure the message is legitimate? Does it contain a link for you to sign in somewhere? It may be a scam. Check your purchases history.

Purchase History Review.