pillow top mattress

I purchased a Simmons queen mattress and box spring from Ashley Furniture in October, 2013.  After it was delivered, I was not happy with it - it sagged on both edges.  I contacted the manager of the store.  He came to my home, looked at the mattress and said that in his opinion it was fine.  It is not fine and never has been.   I believe that I was sold a floor model that had been tried by many customers, which caused the outside edges to wear and sag and leave the center in it's original condition.  The result is sagging on both outside areas and a hump in the center.  Needless to say, I am not comfortable on this mattress.  Can I expect any compensation or replacement for this faulty mattress?