Nighthawk X6 EX7700 no internet issue

So, last week, I received my first copy of this pretty piece of trash.

Spent 15 hours! trying to set up as a wifi extender.

I could easily extend my Wifi and connect to the extender, but my devices either had "no internet", or they didn't receive a valid IP.

In the end, ater chatting with support for an hour and trying wired connections (supervised the extender on my main rig and connected smartphone and laptop to it, both got an IP assigned (in the menu for connected devices) but none received one) and pinging between connected devices (they could not ping each other), I was told to give up, return that chunk and get a replacement.

In the meantime, I found out that there's an ethernet port in the wall in the corner where I wanted to set this thing up.

So I tried that port with my living room rig (HTPC) and, lo and behold, it worked like a charm (200 Mbps down and 100 Mbps up on speedtest) without any setup required.

When the new extender arrived today, I had already decided not to go through the hassle of setting up an extended Mesh network, but instead simply use it as an access point on that network connection.

Oh, how I was wrong. I've spent an hour now, trying to get this piece of crap to work, but it simply won't.

It says that there's a network connection (LED on the right), but the signal for the connected router is off.. ???

Also, in the Nighthawk setup app (Smartphone), I couldn't even connect to this piece of chunk, despite being connected via wifi directly to the extender. It said, I need a new firmware.

Said and done, new firmware installed via computer (192.1.68.1.250 works obviously).

The smartphone still cannoct connect. (With the old extender, I was able to at least do that..)

Long story short:

What do I have to do to set up an access point at a wall socket?

As I said, the internet simply just worked from my HTPC, but the Extender claims that there is no connection to the router. I'm 100% sure that this is not some magical wall socket that goes "directly into the internet", without a router inbetween.

However, I also have no idea, where this connection goes to, because this is a huge network (several buildings linked together, with access points where needed).

If you could help me out here, that would be really great.

P.S.: I'll try and set up an extender in the meantime, but the signal in that corner is really weak.