Therapedic Mattress Review

We Bought the queen size Therapedic Back Rest mattress set.  The first 6 weeks the bed was very comfortable.  I did contact the company because the springs were very noisy.  They said it was normal for the popping and squeeks.  Now the mattress is 3 months old and it has a 4 inch sag in the middle.  I have contacted the warranty dept and they told me to call the store.  I did that and they said someone from the warranty dept will come see it.  I got an envelope with a form to fill out and take pictures to send them.  I have complied and I emailed and snailed mailed that to them and I still have not heard a word back on this.  I previously owned one of there mattresses and it is 9 years old and I love it.  But right now I would NEVER buy another one of there products nor would I recommend them to anyone.