Online port checking tools might fail if your Internet Service Provider (ISP) has placed you behind a NAT, especially if you might be sharing external IP address with other people.
When you used the port checker application were you directly connected to the same router/modem a the Xbox? It would probably help if you describe your network.
Why do you want to port forward in the first place? You have connection issues or something? If you want to check if there's a port forwarding issue you can always put your Xbox in DMZ in your router - this is for daily use not secure and might cause other devices on your network to have issues but it might help with diagnosing whatever problem you have on the Xbox.
PS. please be aware that this is a public forum, not direct customer support - it's mostly gamers helping other gamers (like me right now) - if there's noone there can answer then there's noone that can answer.