sink hole

This mattress is the worst mattress I have ever owned. The sink hole is just getting worse and worse. I called the store to complain, and they sent out two guys to evaluate the problem. They concluded the frame was not supporting the mattress the way it should, causing the "sinkhole". I regret not forcing them to "retest" it without the frame. I got a letter a few weeks later saying its the frame, not the mattress. It has the same problem without the frame, just on the floor. Not only will I avoid this brand, I will never buy anything from that store again. Why have a warranty that just shifts blame away from their faulty product? The warranty guys and their smoke and mirrors "testing". They used string and office supply binder clips along with a paper ring with a ruler. This ring looked like a burger king crown for kids. the sag was VERY noticeable, and they still simply blamed the frame. It was a joke, and a waste of my time.