No internet connection via Smart TV?

I have the following problem. Netflix just does not work for me at all. Allegedly there's no Internet connection or no connection to the WLAN. Although my wireless connection is strong.

Mobile phone can be connected to the WLAN. But not my smart tv.

Every time I try, it means failure.

What else could I do?

I have the power at the router / Connectbox and Smart Tb each for 30 sec. Interrupted.

But nothing happens… What can I do now that my Smart TV connects to the Internet, so I receive Netflix again?

What kind of Smart TV do you have? If it's a Samsung I can help.

This is a Grundig Smart TV… My sister bought me that. Now Grundig wants to send someone out at my expense. The TV is just 3 weeks young.