Frequent unrequested Apple ID verification codes

I have recived message from Apple: “Your Apple Account Code is: ….. Don’t share it with anyone.”

I wasn’t using my phone or other device at the time, and surrely I wasn’t the one trying to log in my apple account. I then changed all my passwords, including for different accounts not related to Apple. After one month, I recived 2 other messages like this. I then again changed all my passwords. After another 2 weeks, I recived another 2 messages. I can’t change all my passwords this often. Also, I checked in settings, and my phone apears as the only device logged in with my apple account, there isn’t any other device on my list. Why is this happening, especially so often? What should I do (and changeing passwords every month or week is not an option)? And should I be concerned? Thank you