What should you do if your email address changed?
If your calendar is hosted on Google, Office 365 or Outlook.com and your email address was changed simply close your account and sign up again. FreeBusy will recognize that the email changed (assuming your company didn't also migrate from one email hosting service to another) and update all references to your old email address with the new one:
Click 'Close Account' button (without cancelling the subscription)
Sign up again here https://freebusy.io/signup
Your settings and history will still be there and it will not cancel your subscription.