Simmons mattress, poor quality and after sales service!

I bought the "top of the range" Simmons mattress, at a cost of over Thirty Thousand Rand, just for the mattress. It soon started showing visual signs of sagging on both sides of the mattress where we sleep. I also wake up with a back ache each morning - something that never happened with our previous "cheaper" brand mattress. As the mattress is still under warrantee, we went back to the store (Dial a Bed Faerie Glen). They sent out someone from Simmons to inspect. The next day a lady phoned us from Simmons, telling us that even though the mattress is still under warrantee, they are not going to do anything about it, because of a coffee stain on the one corner of the bed. (I did spill some coffee a while back, but did not want to use solvents to clean it, for fear of damaging the mattress.) This to me is like telling someone that they will not fix a car's broken engine, because the bonnet is scratched!!! Surely one can expect a better product and after sales service when buying the most expensive mattress in the whole Dial-a_Bed shop!!!!!