Click on this link "If you think your Apple ID has been compromised" --> https://support.apple.com/HT204145
'Checklist: If you want to see if anyone else has access to your device or accounts' click here --> https://support.apple.com/HT212021
Security and your Apple ID - https://support.apple.com/HT201303
Contact Apple for help with Apple ID account security - https://support.apple.com/HT204169 "This article provides country-specific Apple Support contact information for customers seeking help with their Apple ID password or other security-related issues." Better for directly reporting an issue.
Click on this link to learn how to 'Change your Apple ID password' --> https://support.apple.com/HT201355
"After you change your Apple ID email address or password, you might need to update your sign-in information with any Apple services you're using" Click on this link to read "What to do after [or before] you change your Apple ID email address or password" --> https://support.apple.com/HT204071
- If you use the "Find My" feature disable Find My before changing your information, change the information, then reactivate it with the new information.