Welcome to Android Central! It's unclear what you mean by "deleted email." If you did a factory reset through the phone's Recovery Menu (and not the usual
Settings>Backup & Reset menu), that would be considered an unauthorized reset, and would therefore trigger Factory Reset Protection. The phone would require the user to enter the Google account and password associated with the phone to proceed after the reset attempt. So if you completely deleted that Google account (and I mean from the cloud, not just from the phone, like this:
https://support.google.com/accounts/answer/32046?hl=en), that effectively renders the phone useless.
If, on the other hand, you did a conventional factory reset through the
Settings>Backup & Reset menu, that would've properly removed the Google account associated with the phone, and then you could have set the phone up as if it were brand new with a different account.
BTW, the S8+ is over 3 years old, so there'd be absolutely no expectation for Best Buy, Verizon, Samsung, or Google to help.