Sink hole

I'm the princess and the pea character. I loved the mattress for almost 2 years. After that, there has been a sink hole in the center of the mattress. It is slightly noticeable to look at. My partner and I sink toward the center at night. Neither of us get a good night's sleep. The mattress is not yet 3 yrs old. I added a memory foam topper because I occassionally feel a spring poking my hip. Neither of us are sleeping well anymore. We have taken the fabric off the bottom of the box to check integrety.No issue of cracked boards. We have had it on a frame with 3 center supports (4x4s) and 6 deck boards and also a water bed frame. Prior to this I had a Restonic mattress with marvelous middle supports. It lasted much longer than this piece of shit. Neither my partner nor I are heavy people. Mattress was a waste of money.