WNDR3700 and Samsung TV: wifi but no Internet

Hi

I just bought a Samsung smart TV and am now trying to connect it to the internet via wifi. The problem is that it connects to the router but not to the internet.

Other things that DO give an internet connection:
- Ethernet cable to the router works fine.
- Wifi from TV through my phone (connected to internet by 4G) works fine.
- Wifi to my neighbor's Asus router works fine.
- When connected to my router with wifi, the TV answers to ping.
- All other devices connected to my router do have internet access.

So, the problem seems to be with my router...

Things I have tried but without any luck:
- Changing the DNS on my TV from the local one to OpenDns or Google.
- Changing the DNS on my router to the above.
- Giving the TV's MAC address a static IP other than the automatic one.
- Double checked that the TV uses the same wifi encryption as my router.
- Port forwarding of port 80 and 433 to the TV.
- Reset the TV in order to clear it's DNS cache (got help from Samsung support to do that).

Is there anything I could change in the router? It would be nice not having to factory reset the router, since I am not looking forward to go through all my settings again :)