git pull displays "fatal: Couldn't find remote ref refs/heads/xxxx" and hangs up

There are probably some commands to resolve it, but I would start by looking in your .git/config file for references to that branch, and removing them.

You also have to delete the local branch:

git branch -d 6796

Another way is to prune all stale branches from your local repository. This will delete all local branches that already have been removed from the remote:

git remote prune origin --dry-run

I had a similar issue when I tried to get a pull with a single quote ' in it's name.

I had to escape the pull request name:

git pull https://github.com/foo/bar namewithsingle"'"quote