Problem caused by used not the server.
Mod please delete
A good start would be filling out the support post template, otherwise trying to help you will be needlessly difficult.
Beyond that, I don’t know what exact chain of events has taken place. What you describe alone shouldn’t cause that. But, look in your data folder in a folder called __groupfolders and you’ll see numbered folders representing each group folder.
My best guess based on info provided is that your group folder was recreated instead of renamed. If that’s the case, the files are probably sitting there in a numbered folder that’s orphaned or no longer used by any active group folder. If that’s the case, you can figure out which folder has the files and which one is the new one, and you can move them. Then scan the group folder using occ groupfolders:scan <id> so it can pick up the manual changes.