Lumpy mushy uncomfortable terrible terrible experience

We've had our mattress for less than one year initially it was nice , no odors , felt comfortable ,not too warm... At this point again not even a year old the mattress is very mushy , two large holes were my husband and I lay. We have to rock to get out of bed. We both have arm , shoulder , and hip pain. (5.3 145- 6.2 215) We both wake up in the middle of the night or early mornings and get out of bed! We no longer hold each other in bed because that too seems to just fall in. We have been sleeping on twin mattresses in our guestroom on and off for the last month. We have company coming in two days and will be forced to go back into our room and sleep on our mattress, we are not looking forward to that. We had an inspector come out. Just yesterday we found out that they are not going to do anything about our mattress only offer a 20% discount on a new one. we paid $4500 (not including the tax) for this mattress again it's not even a year old. We have never paid that kind of money for a mattress before. Sure wish we hadn't done it this time ! we paid the bed off in just a couple of months and felt so good about that. Now what? Very sad and so disappointed.