Their answer:

  Dear <user>,

  Thank you for contacting FogBugz Support. I understand that you have received a billing notice and do not want to be charged. You may be wondering why you have received this communication and wish to have your account deleted.

  In the first place, please be rest assured that you will not be charged unless you have added a valid payment method to your account. The notification you have received is due to the recent changes to the FogBugz Base Subscription Model. Please accept our apologies for any misunderstanding this may have caused.

  Additionally, be aware that your subscription will be automatically canceled and scheduled for deletion 30 days after the current billing period unless you add a valid payment method.

  Finally, please be aware that trial accounts that were not active for a period of 9 months are automatically disabled, and will result in an Error 500 if you try to access the URL. These customers may have still received a notification despite not having an active account or a configured payment method.

  Since there is no further action required from our end at this time, we will be marking this ticket as solved. That said, if still you have any other questions or concerns with which we may assist, please let us know, and we will be happy to help as required.

  Thank you.

  Best regards,
  <NAME>
  FogBugz Support Team

I had a hard time logging in to get in contact with them. My fogbugz link (for which I should pay) returned 500 Internal Server Error, logging in Firefox didn't work, in Chrome it said that the password in invalid, and I didn't get a reset e-mail (tried twice), I've logged with Google credentials but I got a "This page doesn't exist" on a central-supportdesk.zendesk.com page.