Hello, if the facebook account you are trying access was created with Number A, and you are locked out of it, you will only be able to recovery it using Number A. You can add a second number at this stage. Once you regain access to your account you change your number.
If in this instance Number A is not a valid number, but your account was still created with it, and you can't receive messages through it.... you can try to connect to your facebook account via a web browser, as opposed to the Facebook app. The browser option should allow you to select an alternative means of verification, ie. the email attached to the account.