Change all your passwords on everything. Set up two factor authentication if you have not already:
Click on this link "If you think your Apple ID has been compromised" --> https://support.apple.com/HT204145
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.