@burgerLover 

If you have an ISP modem/router before the C7 which does NATing, to avoid the double NAT you should set C7 in AP mode (Case 1).

When set in AP mode, C7 won't do the NATing.

If that doesn't work for you check if you can set your ISP modem/router in bridge mode and leave C7 in router mode - thus only your C7 will do the NATing.

Probably some ports need to be opened for the particular game as well - this should be done on the device that does the NATing.

@burgerLover 

I assumed that you have an ISP modem/router in your network to which you connect your C7.

If you plug the C7 in your wall socket and you don't have any ISP device before your C7, I wonder where this double NAT comes from.

Who's your ISP ? Is your C7 WAN IP address public or private :

Private IP addresses are in these ranges:

10.0.0.0 – 10.255.255.255

172.16.0.0 – 172.31.255.255

192.168.0.0 – 192.168.255.255

100.64.0.0 – 100.127.255.255 (CG-NAT)