stuck on loading

Hi. I need help please...for 2 days my son has been driving me mad while I'm trying to get xbox working.

His xbox was updating roblox but was stuck on 0% for hours and games weren't loading.

God knows what he was clicking and changing while this was happening.

I've turned it off, restarted, unplugged, reset, signed out of profile.

Now when I'm being asked to sign in, a white loading circle appears for a few mins then dissappears, taking me back to the home page.

I can't open any programs on it, same loading circle appears.

My son's now told me he was messing with something to try 'developer mode'. I have no clue what he's changed or if this is the cause.

Xbox is currently unplugged and I've not tried to start it since yesterday.

I've tried multiple times using the phone support option and it keeps saying 'there's an error on our end. Try again later'.

Any suggestions are welcome�� please

:)