ZINUS Queen 10" True Support Hybrid Mattress

I bough my mattress at the end of December and started using it after December 31st when I moved to my new place. Before placing it in my bed, it spend around a week expanding in the floor, more than the suggested time. I bough extra firm because I have chronic pain. At the end of February, beginning of March it started sinking. I contacted the company for warranty and they agreed to change it, they asked me a few photos and information and told me there were two options, sending a new mattress or prorated refund with the condition of sending them evidence that it was disposed or donated. I told them I wanted replacement because this is the only bed I have, plus I don’t agree to prorated value of a mattress that is warranted for 10 years, but was defective and started sinking in less than 3 months. Is not fair when the client has to pay for the company’s shortcomings and they need to be accountable. Weeks later I receive a message that they don’t have the mattress in warehouse, if I wanted the refund or wait? I once again explained is my only bed, is not an option for me and I would wait. I even told them I would be open to get the 12” even when I paid for 14”, if they had it available. Some time later they ask again the same question. I give the same response and tell them that is unfair they pretend for me to pay for their shortcomings, they are asking for something totally unreasonable, just change it for the smaller, I’m giving them that much grace. Right now, the send an email again that is not possible, if I wanted the refund. I ask them if is still required for me to dispose the mattress? Yes, they apparently want me to sleep in the floor in order to solve a situation their company is responsible for, not me. I also asked what would be the refund and if they cover the tax, because I would still be losing money. They said depends of from what year is the mattress, I have literally sent receipt and said so many times that it started sinking very soon after buying, this is a new mattress. Now they say they wouldn’t cover it because I bought it in Amazon, so now is not depending on the year, when I remind them is only 4 months old!!! I’m just tired at this point. Sleeping with back pain caused by the extra-firm mattress I bough while the company is still asking me to sleep in the floor and lose money to cover their mess-up.