Has anyone else had drain issues on a vauxhall zafira?

My vauxhall zafira started to make a strange noise when driving - as if water was swishing about inside the floor. We found some plugs underneath the car which when we took them out allowed loads of water to be released. So we drained it all out and it then rained that night and the car filled up again! We spoke to vauxhall who first claimed they had never heard of this problem and advised us to come in. When we did bring the car in they suddenly knew all about it and said it was blocked drains and that it was not under warranty and would cost us to be fixed. We took it home and subsequently cleaned the drains ourselves-however they were not dirty so we are waiting to see if the car fills up again tonight or if the problem could in fact be something totally different. we were just wondering if anyone else has had this and if so how they rectified it?