Who is using my Apple ID??

Note that since the fall of 2012, your @mac.com address is nothing more than an alias to your iCloud email account (iCloud: About your @icloud.com, @me.com, and @mac.com email addresses - Apple Support). The only actual or real Apple email accounts since MobileMe was shut down are iCloud email accounts. All @mac.com and all @me.com address stil in use after the fall of 2012 are merely aliases addresses to your @icloud.com email account inbox.

So mail sent to your @icloud.com address are going to go into your inbox, since you only have one Apple email inbox - your iCloud email inbox. The @mac.com address also puts incoming mail I that same email inbox, since that is the only one you have with Apple.

So if someone is spoofing your @icloud.com address, there is not much you can do to stop them doing so. You can login with a web browser to your iCloud account and use the tools in the web mail app to make some rules to dump those emails (based on subject, to or change fields, content) to junk or trash though.

Sounds like someone is purposefully or accidentally typing in the wrong email info and it happens to be yours. I’d continue to use the Unsubscribe option in the emails, notify the sender if not an option, or delete if spam.