Hacked Apple ID

See these security-related documents, especially the first two.

If you think your Apple ID has been compromised https://support.apple.com/en-us/HT204145

Security and your Apple ID https://support.apple.com/en-us/HT201303

iCloud security overview  https://support.apple.com/en-us/HT202303

Ways to keep your information safe on Mac https://support.apple.com/en-gb/guide/mac-help/mh11402/mac

Using app-specific passwords https://support.apple.com/en-us/HT204397

UseTwo-factor authentication for Apple ID https://support.apple.com/en-us/HT204915

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And assuming you are using two-factor authentication, you can Check your Apple ID device list (https://support.apple.com/en-us/HT205064) and remove any device that shouldn't be signed in using the steps in the link.

Use 2FA to protect your Apple ID, read here: Two-factor authentication for Apple ID – Apple Support

Note: Create more than 2 trusted phone numbers, landline can also be used.