Why is someone getting into my iCloud ?

See the following Apple articles:

Recognize and avoid phishing messages, phony support calls, and other scams

Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support

If you think your Apple ID has been compromised

If you think your Apple ID has been compromised - Apple Support

Create a strong password for your Apple ID, It is best if your password consists of eight or more characters and include upper and lowercase letters, and at least one number. You can also add extra characters and punctuation marks to make your password even stronger. 

Never provide your password, security questions, verification codes, recovery key or any other account security details to anyone else. Apple will never ask you for this information.

See also -> Check your Apple ID device list to see where you're signed in

Check your Apple ID device list to see where you're signed in - Apple Support

Remove the device(s) that is not yours.