Body problems of the 2010 Mazda CX9

We took our 2010 cx-9 with 99,000 miles the Mazda dealer in union NJ because of a noise in the car and were told that the rear subframe has rotted out and is destroying the rear diff mounting bolts. We were also told the exhaust system is also rotted out and the vehicle is unsafe to drive. If we go over a pot hole, the whole undercarriage of car can fall out. This car was not kept at the beach and well maintained.