It sounds like you think that you have set up Two Factor Authentication on a Norton account. If you have, then you might have noticed that when you set it up, they gave you TEN single-use securities codes for you to use in scenarios just like this, when you don't have access to your mobile phone number, mobile authenticator application or a USB Security key. So just use one of those ten codes if you saved them somewhere.
Other than that, why not call them if you don't know what you are doing?