The only way I know to do this is to turn off File History in it's Settings (as you did) but then additionally delete the backup off your drive. Then set it up again following:
https://redmondmag.com/articles/2018/03/23/file-history-backup-windows-10.aspx
https://www.tenforums.com/tutorials/55162-turn-off-file-history-windows-10-a.html
That said I do not recommend File History because of the many times I've seen it lose files, often from a terrible glitch where if you to to set it up on the PC you are intending to transfer files to, it can wipe the files out thinking that you are setting it up fresh. Read here how to avoid this:
https://www.techrepublic.com/article/restoring-files-from-windows-10s-file-history/
It's also not as full featured and flexible (as you found) as, say, Macrium File Backup which is unfortunately no longer free like it's superior backup Imaging suite:
http://knowledgebase.macrium.com/display/KNOW/Backing+up+files+and+folders
Here's my latest backup recommendations FWIW:
File History, Windows file and Image backup are dysfunctional and may be phased out in a future version. But they're not the best choices anyway because after ten years in forums I've seen countless times that files are lost trying to restore them, so feel obligated to recommend choices that work better and are more reliable.
The safest and most reliable backup method is to sort your files into their User Folders (Documents, Desktop, Pictures, Downloads, etc) and periodically drag or copy them to external or another hard drive. See tips for copying large groups of files here: https://www.pcworld.com/article/2086566/the-many-ways-to-copy-move-or-delete-multiple-files.html
Then have one other Cloud backup so your files are safe from fire and theft and easily accessible via the internet just like email. Some suggestions to help ease into this habit:
You can drag or copy 5gb for free into OneDrive app to store in the cloud where they are safe from fire and theft. You can also choose to sync the Desktop, Pictures and Documents folders (only) in OneDrive app Settings > Autosave for real time backup.
If you install Google Drive, you can use their new Backup to choose ANY User folders (Documents, Pictures, etc.) to sync up to 15g for free to their cloud in real time. You can also drag/copy selected files into Drive folder.
Besides your files you should back up a System Image to use in place of reinstall in 20 minutes. The best free alternative is Macrium: http://www.howtogeek.com/howto/7363/macrium-reflect-is-a-free-and-easy-to-use-backup-utility/.
There is an easy way to mount the System Image to extract files if needed. Some prefer to move their User folders off of C to make the image smaller and so they stay current if you need to re-image C. Here's how: http://www.dummies.com/computers/operating-systems/windows-10/how-to-change-the-location-of-user-folders-in-windows-10/
This way if Windows ever becomes irreparable you can restore C in 20 minutes from recovery media, and your files will be current and safe in their own separate partition. If they are left on C they will be dated from when the image was taken.
I hope this helps. Feel free to ask back any questions and keep me posted. If you'll wait to rate whether my post helped you, I will keep working with you until it's resolved.