(Source: https://wiiu.hacks.guide/#/archive/cfw-choice )- Don’t format the system while CBHC is installed!
- Don’t delete the user account that bought the DS Virtual Console game!
- Don’t re-install the same game using WUP Installer or from the eShop!
- Don’t install Haxchi over CBHC! (You will not brick, but it will cause a boot-loop! Hold A when booting to access the Homebrew Launcher and uninstall CBHC.)
- Don’t uninstall the DS Virtual Console game without properly uninstalling CBHC first!
- Don’t move the DS Virtual Console game to a USB drive!

You were faster than me. Wanted to write something similar.Did it have CBHC installed? Cause that's what happens when you reset a CBHC hacked Wii U:
(Source: https://wiiu.hacks.guide/#/archive/cfw-choice )
Sadly there's nothing you could do to fix this, esp. as I don't think you have a NAND backup.
idk if they will accept returns but yesI would try to get my money back if you didn't know it was exploited.