I've checked the moderator log, and no-one has removed any threads
Did you receive an email confirmation of your ticket being submitted? If you did, there will be links to the tickets in those emails, and if you could please paste those links here, that would be a great help.
If you did not receive any such emails, then unfortunately the tickets were not submitted successfully
Did you disable it via the options, or via the Add-ons menu? If you disabled it via the options, that would explain why the cron job (where the error comes from) still runs.
Thank you for providing the stack trace, much appreciated. Could you please also include the error message itself?
If you go to the Server Logs page, then click the error log entry, an overlay should pop up that has the error message above the stack trace, for instance
Once I have this information, combined with the stack trace, I will be able to provide a fix for you
Thanks!