Internet connection keeps stopping

Hi ​@Krisztian Pencz, welcome to our community, are these devices connected directly to your modem? (Experia Box) Or through a router or switch? It sounds like there might be an issue with a port or one of the cables.

If you've deduced it's probably an issue with either your KPN Experia Box or the outlet where the KPN cable comes into your house it's probably easiest to give us a call on 0800-0402 or schedule a technician through kpn.com/storing on kpn.com/english you can find more information for english speakers and schedule a call