cPanel access issues can be caused by two things, your firewall or our firewall/brute force protection.
Most business only allow mail and port 80 traffic through their firewalls. This firewall setup causes access to the ports required for cPanel, WHM, and Webmail to be blocked. They might possibly be able to remove these blocks from their firewall.
Ports (standard/SSL)
cPanel: port 2082 and 2083
Webmail port 2095 and 2096
WHM port 2086 and 2087
If you cPanel access was working correctly and suddenly stopped working your IP/username might have been blocked by our firewall. The reason for this is brute force protection systems we have inplace. Please do not run any monitoring services from your client side, our firewall will block your IP for port scanning. If you think our firewall has blocked your username or your static IP then please submit a ticket.