I bought my Serta Premier mattress from Sleep Outfitters in Trussville, Alabama last year, it is only one year old and it is sinking in the middle of the bed, I have a 10 year warranty on it, what is wrong with this? I called the business and they told me that they would be out to see about it, but no reply, so I went to the store and they told me to go online about it. So I want someone to help me !