Can not access from outside LAN

[Karbonaut]

First of all, I realize the topic is almost identical to this:
http://forum.subsonic.org/forum/viewtopic.php?f=2&t=12957
However, my problem is different.

Subsonic works perfectly when accessing from LAN. However, I can't access it from the outside.
My setup:
Subsonic on a mediabox running ubuntu.
D-link DIR-615 router, supports UPnP. UPnP enabled and corresponding feature in network settings in subsonic also enabled. (Status: Successfully forwarding port 17389 and port 18389.)

Subsonic version: 4.9 (build 3853) – January 23, 2014
Server: jetty-6.1.x, java 1.6.0_31, Linux (134.6 MB / 226.4 MB)

Hardware Platform: Linux
SUBSONIC_ARGS="--port=17389 --https-port=18389 --max-memory=512"

Canyouseeme.org reports a connection timeout.
Subsonic reports a timeout: Status: y.subsonic.org is registered, but could not connect to it. (ConnectTimeoutException)
Android app reports a network error.
Browsers from outside LAN can't reach it.

So it seems subsonic can't be reached from the outside. However, UPnP seems to be working, and I also tried disabling it and manually forwarding the two ports. Other port forwarding rules work, so the router seems to be functional. Yet still I can't reach subsonic from the outside. The problem could occur somewhere else too I suppose (my ISP blocks the following ports: 80, 515, 53, 69, 138, 139, 25, 465, 135; But I suppose they might have other blocks in place as well. )
Any hints how I could try finding out what exactly is the problem and where it occurs?

[GJ51]

Turn off U Plug & Pray in Subsonic.

Manually port forward.

You MUST see the port open through Canyouseeme.org before you can reach Subsonic from outside the LAN.

It's always the port forward rule.

Try just getting http access before moving on to SSL.