Kouhei, sorry this happened to you. Someone else mentioned too, but do you clearly have before and after pictures of what your jumbo looked like before and after? So you can clearly articulate to chanel when this change/warp occurred? I would be curious to see photos of the inside, side and bottom, it's hard to assess with the two photos. It's very interesting the warping is mostly on the inner, lower flap, that it's isolated to maybe a defect in that piece of leather. I think you have to lay out your arguments to chanel, 1) if this was water damage from the outside, why is the inner flap most impacted? 2) If this was water damage from inside the bag, why does the sides, and inside look ok but only the one piece of lower pocket affected? 3) if it was a heat, humidity issue, again why is that one pocket impacted?
These are some of the questions that come to mind I would make Chanel answer with the limited views I have of the bag