Within my warranty rights.

I've bought a new vehicle from Renault SA and there is a 5 year, 150 000 warranty on the vehicle. The vehicle is 3.5 years now and the stitching on the driver's seat is coming apart and the warranty department indicated that the interior trim is not covered during the 4th and 5th year, yet they do not want to repair the stitching on my seat even though I am still legally under the warranty time for the interior trims. There is no further damage to the drivers seat or any of the other seats, I have hard evidence to collaborate all my information. Please assist in this regard.