My fiance and I bought our first mattress yesterday. We went to a mattress store and ended up buying a lightly used Florence Beautyrest Black. We were really excited since we got it for 400dlls, so we put it in the truck we had rented and left it on its side for a few hours while we went to get other furniture. Later that night when we finally put the mattress on the bed frame it had a HUGE lump in the middle. We thought this was because  the pillow top moved a little while the mattress was on its side on the truck, so we tried putting the mattress on the other side while trying to smooth out/beat the lump from it. It didnt help much, the lump just moved a little bit.

How do we get rid of the bump? Were we robbed (the bump was not on the mattress when we looked at it and lay on it on the show room, but i cant help and wonder if they sold us something broken)? Any advice would be very much appreciated!