Can't "git push". "Heroku Git error" for 4 days now

Question

As described in the title, I can't push to one of my apps.
"git push" to other apps work fine, so credentials/keys set up is OK.

The error message:

$ git push app-remote

 !  Heroku Git error, please try again shortly.
 !  See http://status.heroku.com for current Heroku platform status.
 !  If the problem persists, please contact http://support.heroku.com.

fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.

I'm disappointed with Heroku support, as my ticket have no answer after 4 days :(

Answer 1

$ git push heroku master

Warning: Permanently added the RSA host key for IP address '50.19.85.156' to the list of known hosts.
Permission denied (publickey).
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.

heroku keys:add fixed this for me