If you're positive P2P is enabled on the cameras (I'd also reboot them, and make sure the P2P still shows as enabled after a reboot), then as others said before, the issue is likely something on his router/firewall/ISP that is blocking the traffic. Make sure the cameras have a proper gateway address and DNS primary/secondary too (from the DHCP) server. You can also temporarily set them the cameras to Static IP and force DNS primary/secondary as 8.8.8.8 and 8.8.4.4 as well. But yeah, likely a router/firewall/ISP issue.