I am having a problem pushing to a different heroku remote.
To check myself I renamed my entire project directory to _backup and then:
git clone acco
I am always a big fan of using git pull --rebase and then git push origin master . A couple of the places I have worked since a lot of places do not allow a push -f (especially places that use bitbucket).
git pull --rebase
git push origin master
The rebase will apply your changes after those already to the remote (online website). This video literally goes over your exact issue and solves it using git pull --rebase https://youtu.be/IhkvMPE9Jxs?t=10m36s