saggy middle

When we bought this mattress set it was supposed to have a 30 yr war. and we were told that the full war. was good for 5 yrs then it would be prorated. We have had this bed for a little less then 4 yrs and in the middle it has a dip in it already. After researching to find a contact number for this mattress co. I called them . I was asked if it had any stains on it I said no. The lady in customer services said that if it had even a water stain were a sales rep could tell it had been wet then dried would void the war in its entirety. I was told of such when purchaced. When we bought this it was 1 down from the top of the line of this co at the store we purchaced bed. I was told that a sale rep would be calling me to set up a time to see this bed. Its been over 24 hrs and Ive still not been contacted. The factory is only 2 hrs from here. I paid over $800 for this bed and got it half price, since the furniture store was going out of buss. It supposed to come with a 30 yr war. against sagging and breaking down yet it didnt even hold up for 4 yrs.