I think I've been hacked!

Check your device list to see if there is a device signed in that you don't recognize. You can remove the device using the steps in the article below. As a precaution, change your password.

Apple ID device list -Check to see where you‘re signed in.    

 Apple ID Password Change.      

 What to do after you change your Apple ID or password - Apple Support     I suggest doing this before you change your Apple ID or password.

Helpwithtechnicalissues Said:

"I think I've been hacked!: I received a message stating that my apple id and name have been used on a new i-phone today. There was no option to contest it. What do I do? I did not purchase a new phone today."

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Reporting to Apple:

Is this an SMS text message? If so, it is a scam. So, report this to Apple. Perform as instructed here: Using the Photos App to Report Scams: - User Tips

https://support.apple.com/en-us/HT204145