I have deleted all the “letsencrypt” directories and and changed the nginx–>sites-enabled–>django settings .. i have changed the setting as ,

upstream app_server {
    server 139.59.31.252:8000 fail_timeout=0;
}
server {
    listen 80 default_server;
    listen [::]:80 default_server ipv6only=on;

#    server_name 139.59.31.252:8000;
    server_name operationscentral.co www.operationscentral.co;


    root /usr/share/nginx/html;
    index index.html index.htm;

    client_max_body_size 4G;
    server_name _;

    keepalive_timeout 5;

    # Your Django project's media files - amend as required
    location /media  {
        alias /home/django/django_project/django_project/media;
    }

    # your Django project's static files - amend as required
    location /static {
        alias /home/django/Insights/staticfiles/;
    }

    # Proxy the static assests for the Django Admin panel
    location /static/admin {
       alias /usr/lib/python2.7/dist-packages/django/contrib/admin/static/admin/;
    }

 location / {
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header Host $http_host;
        proxy_redirect off;
        proxy_pass http://app_server;
    }
}