Someone is using my iCloud, how to remove them permanently

Change your password and enable two-factor authentication. https://support.apple.com/en-us/HT204145

Hello ~ After going to the link *muguy* provided and changing your password plus enabling two-factor authentication as suggested…pay special attention to *Make sure your Apple ID is secure* section thus preventing this from happening again. Keep your info to yourself :) Also take a look at link below if you want to safely share:

Family Sharing - Apple

~Katana-San~