Power Steering Failed problems of the 2015 Mercedes Benz ML350

The vehicle was in reverse when a strong sound was heard coming from the back, after starting the car, it displays a warning message light on the dash; it became difficult to maneuver and a squealing sound was heard coming from the engine, this could easily have resulted in a loss of control and a crash without any warning. Immediately mbrace was contacted and the vehicle was towed and taken to the dealer where it was diagnosed that the power steering control failed and needed to be replaced without warranty and at my own cost. They accused me that the car must be involved in an incident/accident, but it is totally impossible for the car to have suffered a heavy blow, or to have gone into a hole, or to climb a high sidewalk, etc. Without a sign of damage; the damage piece (steering gear) is located in a place that would be totally impossible to reach without the car suffering a heavy impact, which would have caused an additional external damage below, or in the tire, bumper, rim, or any other part, even the air bags. The car externally including each single part, is in perfect condition. This damage was not caused by anything that I did wrong; must be a defective part from the manufacture, and I can't not assume responsibility of this. The mb USA was made aware of the failure, and they insist that I have to pay for it or my car insurance needs to be responsible monetarily of this situation, which is completely unfair to me and should be covered by the warranty. It has only 18,000 miles approx. And I shouldn't have such a serious problem with this brand at such low mileage. If a defective driving part in the steering gear exists in the vehicle, that causes it to break during normal vehicle turning, the normally available hydraulic support function will no longer function and steering wheel operation will be limited.