This is a malfunction for which you best call. This can be done 24/7 with a malfunction. The VRS understands English.

The free of charge number is 0800-0402 ( <- tab on mobile to call)
Malfunction 24/7

Other:
monday - friday 08:00 tot 18:00 uur
saturday 08:00 tot 17:00 uur
sundays and holidays closed
Or let kpn call you back.

Have you tried to turn the modem off for 3 minutes en then on? With the white (press) button on the rear.

Hi ​@Jarek203 , there are issues with some of the power adapters supplied with the KPN Box 12, causing the modem to go into a restart loop. Contact KPN as ​@PeterG suggests.
Some customers obtained a replacement in a KPN shop.

Hello,

thank you for helping me solving this problem. I went to kpn shop and I received new router. Now I have to install it. How to do it? 

Just connect it. It shall automatically load the software.