how to remove a file from git to never exist at all

so i pushed a ouath key file into my git branch from my local copy. how do i overwrite commits in git to remove the oauth key file?

i tried doing

git rm cache /storage/oauth.key and did a git add, git commit, git push to my branch but the file is still there.

i also tried doing

git revert commitID but got an error

error: commit 5ac87ad863059396jkljkljlkjce4c64 is a merge but no -m option was given. fatal: revert failed

please advice.

via Chebli Mohamed