How could someone get into my Apple ID???

You might want to consider changing your password and making sure it is a strong one. You can also add 2 Factor Authentication to your account for more security. If the attempts continue, you might want to consider a name change.

 Apple ID Password Change.     

Note the restrictions in the article.

Apple ID Name Change.        

 What to do after you change your Apple ID or password - Apple Support    I suggest doing this before you change your Apple ID or password.

Apple ID -Two-factor authentication          

Two Factor Authentification availability.     

Apple ID - Using app-specific passwords.     

Apple ID - Two Step Verifications FAQ    

It is not easy to hack an Apple ID account (Note, however, that some are scammed into giving away their Apple ID passwords.). Still,

See these security-related documents:

If you think your Apple ID has been compromised https://support.apple.com/en-us/HT204145. From the link, among other things, Change your Apple ID password and choose a strong password.

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

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

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And, if 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.

If there are none that shouldn’t be signed in, then you should not have a problem at this point. But, if an unauthorized device is signed in, Change your Apple ID password https://support.apple.com/en-us/HT201355 

Here is What to do after you change your Apple ID or password https://support.apple.com/en-us/HT204071

For Apple Support help with your problem, use:

Get a call from Apple support to help solve your problem using this link https://getsupport.apple.com/?caller=kbase&PGF=PGF63005&category_id=SC0245&symptom_id=23362

Apple ID Support https://support.apple.com/apple-id

Apple Support Twitter  https://twitter.com/AppleSupport

Apple ID account security for country-specific and region-specific help https://support.apple.com/en-us/HT204169

Get Support: We’re here to help https://getsupport.apple.com/. Go through the options to find the best support option.