It would appear that while you’re able to access your Django instance directly on port 8000 your web server is not configured properly to proxy those connections when you are trying to access it via port 80 (the default).
Which web server are you using? Nginx or Apache?
If you can share your site configuration (/etc/nginx/sites-enabled or /etc/apache2/sites-enabled) we can likely help you make the adjustments needed to access your site on the default http port.
Once that is working you’ll likely want to change your Django setup to listen on 127.0.0.1:8000 or localhost:8000 (this way it would only be accessible through the web proxy and would no longer appear on port 8000 publicly.