Mattress Firm

We purchased our king size pressuresmart firm mattress from the Mattress Firm store located at 38 Nardozzi Place, New Rochelle, New York on January 23, 2001 and received it in our home on Febuary 21, 2021.
During the purchase transaction, we also purchased the protective covering and was told to have the delivery people slip it on as soon as the mattress was delivered. And we did so.
Over the next few months the mattress started to sink on the sides that my husband and I sleep on. It is now to the point that there is a large "hump" in the middle of the mattress.
Once we noticed this I called our sales representative and told him of the issue. He told me to take the protective covering off and take pictures of the mattress as well as the tags. At that point we noticed a cheese doodle shape/color stain at the foot of our mattress. Now this was the first time we saw this and immediately told our store representative. He then told me since there is a stain it is out of his hands. Insinuating that we caused this stain! This would be impossible since the protective covering was installed immediately. So at that point I filed the online claim. This was on July 26th. (I have both pictures and claim #). We were told that we should receive a response within a couple of weeks. We then tried to call the store location that we purchased and seems they know my number and ignore my calls. I also tried to call the number's I find on the website and internet and all of them have same recording to submit the claim, which we did. It is now August 23rd and haven't heard back from anyone. Please help. It is continually getting worse. My husband and I feel we received a refurbished mattress which we distinctly asked about that and the representative assured us that that would never happen. Our claim# is [protected]. Our representative is also the store manager, his name is Kwabena Akyeampong. Respectfully, a very disappointed customer.