Stearns and Foster / Defective mattress

From June through October I have tried to get Stearns and Foster to honor their mattress warranty. After 5 months of use the pillow top material has shifted toward the center of the mattress resulting in "crowning" (Stearns and Foster words). The effect is that you feel like your laying on an incline and rolling out of the bed. S&F suggested that we lay in the center of the bed when reading or watching TV( we do neither of these). In effect this response by S&F is an admission that there is a problem with the mattress but this defect is not something they choose to acknowledge under their warranty. The mattress has since been discarded and replaced with another brand.