Size of /Users folder is way too low, where is my data?
Finder is probably just counting the /Users/Shared folder or other public folders. You probably don't have permission to the folders containing data for the user, so even though the data is there, Finder can't enumerate it to calculate the size. All you need to do is navigate within the Users folder and give yourself permission to the inaccessible folders (e.g. Documents) with Get Info.