Netgear nighthawk X4 R7400 Not portfowarding HELP PLEASE!

[#1]

So for a while i've had portfowarding problems. I used to be able to foward no problem but for some reason now I can't portfoward atall.
I have tried restarting my router, using 3 diffrent routers, tried fowarding diffrent ports, using diffrent machines, turning all firewalls and antivirus off etc but it just does not foward.
On the router that plusnet gave me, the TG 500 there was an option to put my computer in the "DMZ", and when I did this evreything was fine, ports would foward. Also on the TG500 I noticed that sometimes if I fowarded the same port TCP and UDP seperate, it would work. For example if i selected both TCP and UDP for the port 7777 it wouldn't foward, but if i did TCP and UDP seperate it would work.
However on my new nighthawk I tried fowarding TCP and UDP seperate and nothing changed, still didn't work, and there's also no DMZ option ( as far as i know that is ) so i'm kind of stuck what to do. I would rather not change back to the plusnet router because this router was like 150 pounds and it's much better.
Any thoughts ? Would greatly appriciate

[#2]

Did you mean to say you have a Netgear R7500 ?
How are you testing port forwarding on the Netgear?
fwiw, the R7500 does not appear to support loopback with early firmwares.
Have you updated the firmware?
You may get an answer if you post your question on the Netgear forum
http://forum1.netgear.com/forumdisplay.php?f=170

[#3]

Hi Valsplants
I'm currently having the same problem getting any port forwarding to work with my Netgear 7500.  I have flashed it to the latest firmware V1.0.0.94 and the release notes there say that a factory reset should be performed after that (although I think this has more to do with wireless settings) so I'm going to try that next.
To answer a question in your post, there is a DMZ setting to be found in Advanced > Setup > WAN Setup > Default DMZ Server
I'm trying to get into my home network on port 1723 from outside, which eventually I'll do with VPN but for now I'm just testing with Telnet to prove that there's something listening.  This all worked fine with my previous  Plusnet Technicolor Gateway and the only thing that's changed is the move to the Netgear router.    While inside my network I can telnet to my VPN server on port 1723.    Externally I can ping my external IP address fine, but Telnet shows no response and "Probe my Ports" shows that port as being stealthed.
Interestingly the Netgear logs (Advanced > Administration > Logs) shows the attempt, and that the correct destination and port are being mapped to:
[LAN access from remote] from 104.X.110.211:33964 to 192.168.1.76:1723, Friday, July 24, 2015 10:57:10
But I detect no evidence of the traffic actually getting into my internal network, including checking with a packet sniffer.
Best Wishes,
Peter