Why does my account keep getting randomly locked

I have played games for a while, and when I got my Microsoft account, I had to start paying money. Recently however, I keep going offline for long periods of time, and when I get back online, I notice that my account is locked, and I have to put in a phone number. I when I get my account back, I log off for the night, only to log back on the next day and notice my account has been locked again! I don’t play online, unless my friends are on, and even then I don’t use hacks and I’m not talking in chat. I don’t have 3rd party apps, and I usually only play on Minecraft’s solo worlds by myself. I feel like I’m being restricted from playing my games entirely, because of my account getting locked. I want to know why it’s getting locked, and if it’s possible to stop getting it locked over and over.

:)