I understand that it added extra stress to your travels, but you were given good advice up-thread, which you seemingly decided to ignore. When landing in DUS, you should have followed the transfer signs. According to their website, a non-Schengen to non-Schengen transfer only means a security check; it does not involve passport controls.

Your bags were checked through to NCL, but you were missing the boarding pass for your last segment. Stuff like this happens when you have multiple carriers on one ticket, but it's not the end of the world, BP's can be printed off at the transfer desk or gate.

Feel free to stay on the line, but I'm not sure what you expect the SEN line to do; in their eyes, you are a no-show for the DUS-NCL segment.