My back is killing me

I bought this at mattress firm two days ago. My sciatica is acting up, it's been fine for years. My mid back was sore all day yesterday and my wife's back is sore today (She didn't want to try it the first night). She does not want to try it again. My back and hip are bothering me today. This bed is stiff!!! The sales lady sort of pushed me towards this mattress. I wanted to bring a mattress home that day, mistake. She didn't have a mattress in stock, so she said she would sell the floor model as new, as it hadn't been on the floor long. She never told me the warranty or return policy, except that she would honor the 120 day trial. When I looked up mattress firms return policy, they don't return display mattresses. She put display on my receipt, even though she charged me full price $ 1599 minus a $ 300 that she called a price match. She looked up price match on the computer. I'm going back today to try and get this straightened out. The mattress is very firm, I'm wondering if they bagged the wrong mattress for me. Anyway, I'm not happy, $1430.75 , and the worst pain I've been in in years.