There seems to be a problem with the case lookup tool under the 'My Active Request' section of the support page.
It fails to find any case that is closed:
This case number is definitely valid:
@WayneSchrock the web team have this on their roadmap to fix in July. In the meantime, you can view any case using the direct Case tracker URL and appending your case number: https://support.ptc.com/apps/case_logger_viewer/auth/ssl/case= for example: https://support.ptc.com/apps/case_logger_viewer/auth/ssl/case=98765432