Bill thinks his network has been infected because his email won't let him send anymore. It's completely missing. Leo says to make sure the SEND port is correctly configured in the email client (in this case Thunderbird). It's the SMTP server and it usually runs port 587. The scam came from "Spectrum" and "Thunderbird Help" that said he was having a driver issue. Leo says that's a scam. Email doesn't use drivers. It just uses an internet connection.
Leo suspects malware has infected him and it's likely the "helpline" was a malicious employee working on the side, sending Bill to a malware company. He should call Spectrum and report it.
And the fix now is to back up data, wipe the drive and reinstall Windows from a known good source. It's the only way to fix it. Change all passwords.