See this on how to regain control over a compromised apple account
- Change your Apple Account password. Make sure that you use a strong and unique password.
- If you can't change your Apple Account password because it's already been changed by someone else, reset your password.
- Go to account.apple.com to update any of personal or security information that isn't correct or that you don't recognize.
- On account.apple.com, select Devices and remove any devices associated with your Apple Account that you don't recognize.
- Check with your email provider and cellular carrier to make sure that you control every email address and phone number associated with your Apple Account. For example, check with your cellular carrier that SMS forwarding hasn't been set up for a phone number associated with your Apple Account.
If you can't reset your Apple Account password or sign in
If you can't reset your Apple Account password or sign in to account.apple.com, go to iforgot.apple.com to start account recovery and regain access after an account recovery waiting period.
Learn more about account recovery
See this link for further reference
If you think your Apple Account has been compromised - Apple Support