Check to see if you have read-write access.
The Git error message is misleading. I had a similar issue. I had been added to an existing project. I cloned it and committed a local change. I went to push and got the ERROR: Repository not found. error message.
The person who added me to the project gave me read-only access to the repository. A change by them and I was able to push.
I had the same problem, with a private repo.
do the following:
remove the remote origin
git remote rm origin
re-add the origin but with your username and pwd with writing privileges on this pvt repo
git remote add origin https://USERNAME:[email protected]/username/reponame.git