The firmware on this D-Link model appears to be a bit iffy.
First of all: You have to change the internal web-server (the config page) of the router to use a different port-number. Otherwise that gets served first.
(It might be enough to just disable "allow access from the internet" to the config pages. I'm not sure about that.)
Second: That D-Link of your doesn't do NAT reflection.
In layman's terms: You can't access the outside ip-address from the inside of the router.
You can access it just fine from any other computer on the internet.
This is a bit of a nuisance but not a show-stopper. It just means that you need to route your traffic (from the inside) so that your router sees it really coming from the outside.
You need a proxy for that.
It is exactly the same method as used to access web-sites that limit their content to a specific country or region, while you are from a different region. Google for "free proxy BBC iPlayer" and you will get plenty of information how to do this.
Last, but not least: A firmware update on the router may help. These sort of issues are sometimes fixed with an update.