Microsoft account locked and the recovery form won't submit

For a locked account (the suspicious sign-in kind) the code doesn't have to go to your old number. On the unlock page there should be an option to enter a phone number, and any phone that can receive a text works, even a friend's. That's normally the fastest way out and you skip the form entirely. If you do end up on the recovery form, the error at the end is often the browser. Try a different one with extensions off, or a private window. And fill it in from a PC and wifi you've used that account on before, plus give as many old passwords and recent email subject lines as you can remember. That's what it scores you on.