Brake Master Cylinder problems of the 2011 Hyundai Equus

I was driving the hard and I had to come to a stop on the highway. All of a sudden my brakes turned spongy and I swerved to miss a car. I have had the master cylinder replaced thinking that was the issue but it was still spongy. I then noticed the recall on the genesis and I contacted Hyundai. I asked did the recall affect the equss seeing how they are the same part numbers. They told me no and it didn't fall under the warranty either. They said I would have to pay around $2800 to have it fixed. I don't understand how the same part goes bad on 2 different cars but the recall isn't for the Equus in the same years as the recall on the genesis.