I need help with the App Store

I need help with the App Store. My OS versione is 11.3; I need help because some days ago I changed my ID password and now when I want to download a new app, it won’t let me do it. It says that I have to put a code to verify that that’s my Apple ID but it doesn’t let me put it in. In fact I didn’t even receive the message. I don’t know what to do. I tried to change again the password but it won’t work. I tried to put again my phone number but it won’t work. If you know what I should do please help me.