Renault Kangoo enters water when it rains

Hello everyone. My vehicle is a Kangoo 1.5 DCI 70 (65 hp) van of 2005. When it rains (the vehicle is parked) I flooded the floor of the cabin (driver and companion) and the parts below the seats. In the workshop they do not find the origin, they say that perhaps because of the roof plugs, but I have sealed them and remains the same. Could anyone give me a track?
Thank you and greetings to the entire forum.