Hatchback/liftgate Support Device problems of the 2001 Chevrolet Silverado

2001 Chevrolet Silverado has broken tailgate straps and I was informed by gm to call my local dealer immediately and have them replaced. Kool chevorlet of grand rapids would not honor this, and told me I would have to purchase them. When I asked what happens if it false off they said it was GMC problem . Saftey is obviously not a concern here. I called to make a appointment like my gm documentstated and they stated that I would have to purchase the straps and stated they would still have to be replaced because they were defective.