Re: "Need help asap:
See how to: Get help with security issues - Apple Support
For iOS 26: See how to: Manage information sharing with Safety Check on iPhone - Apple Support
and
Control what you share on iPhone - Apple Support
If needed: see the Stay safe guide.
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Re: How do I find out who a iCloud belongs to I’m receiving threats from a iCloud user account that I don’t know "
Learn what to do if you receive suspicious emails, phone calls, or other messages.
See: Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support
Privacy safeguards may not allow for identifying a particular person who could be known or unknown to you: However iCloud Support has a
"Get support = start now" link at bottom right on their website: (online chat / phone / email etc,)
iCloud - Official Apple Support