Restore Whatsapp chat and data
Check the app you used to backup your internal memory. There should be a restore button in there that will restore the folders back to their original locations. You may have accidently backed up your apps instead of your settings/folders. If you did, then your data is sadly permanently gone. There may also be a setting in the app that lets you choose internal or external storage. I don't use Whatsapp so I don't know if there is, but if you do see the option under the settings, you may just need to switch it from one location to another so it can see the folder you backed up. If you could provide a little more data on how you performed the backup (what app you used, etc.) it would help in troubleshooting the issue further.