If you bought a family wifi access from KPN during holidays in Nederlands, you could have issue to logout from hotspot.
Basically, up to 4 devices are allowed at the same time, so you need to disconnect to use other devices. But, if the logout page disappear from your browser, you are stuck.
The solution comes from excellent @kpnwebcare Twitter account, you just have to connect to this link :
And that’s all, you do are logout.