warranty is not what they proclaim

my mattress 1800$ just for the mattress in 3 years has significantly sagged i paid them 35$ to come out and see it the guy in front of me measured a sag of 7 inches deep into the bed and 4 inches high. when they came out he took some photos and noted some light stains that were not anywhere near the sag. I now get a letter that says the sag was measured at 1/4 inch (what a joke) and because of the light stains they have voided a 25 year warranty (do they really think people do not get stains over 25 years of usage). I told them up front it had a few light stains and asked if I would get turned away they assured me that I should pay the money to have it inspected why would I throw 35 dollars away for no reason this was significant sag and manufacture defect. in there letter they proclaim they have a very low return rate du to factory defects thats because they do not stand behind there products. please save yourself some money and do not buy into there sales pitches you will not be happy if you have any defects you will be stuck with a mattress worth nothing