MacOS High Sierra password stopped working

After updating my 2015 macbook pro to High Sierra, I got prompted to enter iCloud options. As I do not have any use for iCloud, I choose to disable iCloud and create 'separate password'. After doing that, I could not login onto my computer at all, using either password.

I tried to use recovery menu, and surprisingly, it was completely useless.

Time Machine => It asked hard drive password, which I have no idea and none of my password worked.

Re-Install OS => It asked hard drive password, which I have no idea whatever.

Terminal => Reset Password

It seems to be working, but when I entered new password, it showed 'Internal Error'

This is a surprising glitch, and it effectively shut me off from my own computer.