Try CheckDisk. I lost 113GB on a 245GB drive and over 500GB on a 2TB. Deleting VSS/System Restore did nothing. Rolled back with RollbackRX to no avail. SpaceSniffer showed me only 62.4GB in use on C:. Checked the larger partition and voila! Got my free space back. Hopefully same result will obtain for C:.
Good luck!
PS: Death to VSS! lol