Beautyrest review: Mattress poor quality

I bought two Beautyrest Silver twin mattress in Macys, the total invested was $2,000. Five and a half years later the mattress condition does not allow one of them to be used anymore. The compression in the middle of the mattress makes it extremely uncomfortable to sleep. You can actually see the difference from one mattress to the other, I can estimate at least two inches below on the middle, looks more as a "hammock" than a mattress. The other one is already showing the same problem but less. I contacted the Manufacturer to claim the Guarantee, they did an inspection and determined that its a "normal impression" not covered by the Guarantee. I have bought Beautyrest mattress many times, I still have one that is 15 years old and is in much better shape that the ones bought five years ago. Cheap materials and a "Guarantee" designed to mislead the customers. There is no such thing as a "Ten Year Guarantee", they find the way not to assume the responsibility and leave the customer with a mattress that is a total loss and that has to be thrown to the garbage.