Hello @Qinthara Aghnia
Maybe you pressed the powerbutton next to the powersocket on the modem by accident when plugin in the powerconnector and the modem is now switched off?
If that isn't it then call the KPN customer service 0800-0402 again and say that you want to speak to an employee.
I tried to pressed the power button in the modem several times but still the modem shows no lights
That’s unfortunate, the only option is calling the customer service 0800-0402, for a malfunction it should be available 24/7.
Welcome to the community @Qinthara Aghnia, that is a very odd situation. The quickest way is to call us like GeSp said, the customer service should also speak English. The robot is only in Dutch, but when you explain the situation it should put you in touch with a colleague. Have you talked to one yet?