brew installation error : Appears homebrew is already installed

I had the same issue. There was no directory called., /usr/local/Cellar but brew installation kept reporting it is already installed.

I resolved the issue by doing the following.,

Step 1 : run

  rm -rf /usr/local/Cellar /usr/local/.git && brew cleanup

(It reported error and didn't run successfully., but I believe it did cleanup)

Step 2 : Being from Windows world., restarted the terminal

Step 3 : Ran again

 ruby -e "$(curl -fsSL"

It ran successfully.,