Lastman's Bad Boy Superstore

I purchased a jackman bassett kingsize mattress and got it delivered on 13 June 2014 I slept over it for 2 night of 13th and 14th had problems with my back so called badboys on 16th morning.. the executive was rude and said we cant pick up the mattress as I dont have warranty.. Now the sales person who gave me the mattress gave me 5 years anti spill warranty but not sleeptrust warranty where I could return the mattress. The problem is instore you could sleep down for 5 mins and it is difficult to understand where that is firm enough for your back or not. They say its the final sale and cant be done anything. I offered them as I want to buy a firm matteress, I am fine with paying the delivery charges and the difference between the new and this mattress if any. I also ordered sofa from them for which I have taken extended warranty for 5 years. When I called their service delivery department I felt I committed a horrified crime by asking them to exchange the mattress with difference paid by me. I feel helpless please advise thanks