It's been very common those days that people can't access their cPanel account within their company network because the IT supervisor's open port 80 only for internet access.
That causes problems when you try to access your cPanel account but ...you can try accessing your cPanel the following way.
Access cPanel behind company proxy firewall
To access cPanel behind your company firewall you can go to http://cpanel.domain.com, replace the domain.com with your own domain.
By using this technique we are bypassing the port on our server, and accessing the port 80 over cPanel.
Hope that works for you!