Indentation/Sagging after 5 nights

After 5 nights of sleeping on this new, not so cheap mattress, there is a butt indentation. Emailed BeautyRest, gave them information (no copy of receipt), and they emailed me back in 2 business days. They asked for tag information (already sent a photo) and a copy of the purchase receipt, then one or two days later told me to contact the store where I purchased it. Store never answered my email (their preference), had to call them and waiting on a 3rd party to come out and look at it.