Can't get into my account

I moved country and changed my phone to a UK number, so when I try to sign into my account I can't receive mobile confirmation text. The option to change my number doesn't work as it doesn't accept my new UK number (only seems to accept my old number to send a text to confirm it's me, but that number is no longer in use). It doesn't recognise my new number as legit, and when I've tried the page to update my number before signing in, it doesn't recognise my old number as mine for whatever ungodly reason.

The only option is to "try and sing in a different way," which then takes me to a never-ending loading screen. What else can I do other than making a new account (which I don't want to do).