Sealy fails at a goods night rest

My husband and I bought a bed roughly 18 months ago- with a new bed I understand it takes 6-12 months for a mattress to settle. Due to us selecting a extra firm bed- we gave it 18months. We have followed all the care instructions. And still this is the most uncomfortable bed I have ever slept on. The Mattress feels nothing like the one in the showroom. I understand that the density of the foam differs depending on the time of day, season and temperature when the mattress is manufactured, this seems to be totally disregarded by Sealy when I brought this up with them. This mattress was expensive, and nothing to sniff at, I have just been told that it is still setting- and to continue with the care instructions that we have been following meticulously! And should we still be unhappy in 6-8 weeks to take it up with the store that we bought it with. Sealy we have done that and due to the warrantee that it was sold with we have been referred back to the manufacturer- and no assistance. I am mortified and will never buy a Sealy mattress again and will warn people on risks involved buying an expensive mattress from Sealy.