If the process Windows used was chkdsk there is a good possibility those files are gone. Are there any chk files in a folder called found.000 on the root of your external hard drive disk?
A poster who had a somewhat similar problem with Windows 10 albeit chkdsk did not run or complete they were able to recover files in the zero byte folder using a live linux disk. You may need to disable SecureBoot and also enable Legacy or CSM boot in order for the live linux disk to boot.
Burn an iso of Fatdog64 to a CD by right clicking the iso file and selecting Burn Disk Image. Boot to the fatdog desktop. Connect your external drive. A USB icon will appear in the lower left of the desktop next to your hard drive partitions. Click once on the USB icon, the disk will mount, and a File Manager window will open. Click once on any folder to open it. If you can see your files in the opened folder post back and I will give instructions on copying files from the external drive to the internal hard drive. Hopefully if you do find them they will not be corrupted.