Can't login to icloud account through settings

This started the other day:

I keep getting the Apple ID Verification message that says "Enter the password for _______ (account name) in Settings". Keeps coming up every few seconds, over and over again, but whenever I go to settings and sign in it doesn't work. It has the loading circle icon, but after doing this it just brings up the verification message again.

I am not having this issue on my other Apple devices though, they are logging in with absolutely no issues, it is just the iPhone where it is not working.

As a result I'm unable to use the App Store etc.

Since this started I have:

• Updated IOS
• Reset my Apple ID password
• Reset all settings on the phone
• Force reset the phone

But none of those have worked.

Also all of my phone contacts disappeared, as well as my email accounts no longer being linked in the mail app, and it will not work when I try to add these accounts back.

What else can I try to fix this because it is incredibly frustrating?