The github username and token in the gitconfig is only used for interactions with the GitHub API (for instance the hub gem and the github tool).
If you are pushing and pulling from a GitHub repository over https, then you need to specify your credentials every time, or hook into a password manager to remember the credentials for you. How to do this depends on your platform.
The easiest thing to do is to go to your github account and submit your SSH public key to your account, and then switch your github remote to push/pull over ssh instead of https.
[edit] After re-reading the question I noticed that you mentioned it was previously a GitHub repo that was just moved from one owner to another. If that's the case, and you ARE able to push and pull by specifying your credentials, it sounds to me to be one of two scenarios:
- The previous remote used ssh, and GitHub has your SSH key; but when the owner changed and you updated the remote, you updated it to go over https.
- The previous remote used https, but you had a password manager setup correctly to deal with your credentials, which no longer works.