Hello everyone.

I'm living in Denmark, but I've bought the TL-MR3420 router in Poland (I'm saying it just in case). 
Yesterday I bought the Internet package from Danske Kabel TV and they declare that I should have been given Internet within 5 minutes.
As I woke up today and called them (since I still didn't have Internet), I figured out that the problem is with the router and (as the consultant described) it was constantly switching itself between being connected to the network and not (I don't remember it clearly but it surely was something like that). Connecting my laptop directly to the wall net plug (with net cable) proves that the problem is neither with my laptop, net cabel nor wall net plug. 

Right now (when the router is connected to the wall net plug), I am seeing on my laptop that I am connected to the router (WiFi), but there is no Internet. 

I also want to underline that the LED lights on the router indicates that Internet is received from the net cable.

What should I do right now? 
I was following the set-up instructions and I don't want to spend my money on the new router.

Please, help me!