I'm having a problem with an HDD that is no longer accessible. I'd like to point out that I'm not a skilled technician when it comes to computers, but I know enough to assemble and install my own PC.
Situation: I wanted to do a fresh install on my PC (new C-drive) so I copied the files I wanted to keep onto a separate HDD (4TB, drive letter H). After the fresh install I started copying the data back to the PC, 1 folder took particularly long and for some reason it had stopped during the process (without my intervention). After the PC rebooted (on it's own) the H-drive was no longer accessible, I received this error:

I tried running chkdsk H: /f /r /x, but it stopped due to an "unspecified error". I downloaded testdisk and let it analyse the disk (took almost 4 full days) and it found 2 partitions, both with same "start" and same file list, but different size. Both were marked D(deleted), so I marked the biggest as primary, the NTFS were both intact but not identical, I copied the boot to the backup boot.
After this the drive was still not accessible in windows, but in testdisk I could see the fileslist. I then tried to mount the disk on Ubuntu but also got the message that the disk needed to be repaired. Trying to repair it under Ubuntu resulted in this error:

Does anyone know what else can be done to repair this disk? There are some folders that I don't really mind to lose (but I'd rather not) because I can download them again, but there are also pictures I took that I don't have a backup. Yes I know it's stupid, but I had 2 drives in mirror prior to the fresh install, I formatted those to get rid of any clutter or undesired files and put everything back, but I never got to that last point.