After you made the settings and rebooted the router, did you network reset the xbox configuration, turn OFF then back on then check NAT status?
Do a network factory reset of the xbox console:
1. Press the Guide Button on your controller, go to Settings
2. Select System Settings then Network Settings
3. Select Wired Network or your wireless network when displayed
4. Select Configure Network then Additional Settings tab
5. Select Restore to Factory Defaults then confirm when prompted.
6. Turn Off the xbox then turn back on.
What generation xbox do you have? 1st gen 360? 2nd Gen Slim, 3rd gen E series 360 or Xbox 1?
What is the WAN IP address that this router gets from the ISP modem or ISP service? Look at the routers status page and let us know if you see a 192.168.#.# or a 172 or maybe a 10.10.something here.