I do understand the privacy-defending angle here, but since the numbers are one-time-only and can not be used later on, then, this looks like it is more useful

I do understand the privacy-defending angle here, but since the numbers are one-time-only and can not be used later on, then, this looks like it is more useful for hacking/spoofing/scamming. I was hoping this would be the same as simplelogin.io, only for SMS, but it's not. What happens when the service needs to re-authenticate and you don't have access to the original number anymore?