I can't help with the cli resize, but perhaps you can delete your apt cache to free up some space on /. All your downloaded packages get kept, and it can take a tremendous amount of room. sudo apt-get clean will delete those packages. apt-get autoclean is a bit more conservative, as it only removes packages that aren't available anymore. Your choice, but I always use clean.
The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore, all progress depends on the unreasonable man.