• Try to log in to my ISP’s website. “Username not found.”
• Try the password reset link and put in the username just to see what happens. “Password reset email sent.”
• Email turns up. Click the link. Type a password. “Password reset successfully.”
• Try to log in to my ISP’s website. “Username not found.”

Edit: to be clear, I didn’t put in my email address, I only put in the username. The system looked up the username and found the email address by itself.