In the event of this happening, give us a call. But, you may be able to resolve the issue.
If your number is right but you are unable to complete the extra checks, this may be caused by your network provider blocking the call. If you think this is the case, please contact them.
Similarly, if you have multiple browser sessions open, make sure that you only have 1 session open. If you are able to receive the call but your code is not being accepted, make sure you only say or input the code when asked and do not say or press anything else.