It looks like you are trying to push using "smart http(s) protocol", which GitHub now supports.
Let's suppose here you have no proxy issue, or firewall problem.
What is your remote upstream repo address?
(what git remote -v show lists?)
I would recommend:
- making sure using an address like: https://gitbug/username/repo.git
- having a
~/.netrcfile with
machine github.com login your_github_login password your_github_password
- try cloning again your repo
git clone https://github.com/your_github_login/gitrepo.git, and push through that instance.
Note: as Noufal IbrahimNoufal Ibrahim comments, you could use ssh (unless ssh port is blocked, leaving you only with http/https connections)
git clone ssh://user@server:project.git