Collapsed mattress no help

We purchased a bed and mattress from The Bed Shop in Roodepoort with a 5year warranty on the mattress. Not even 1year later the mattress collapsed on the one side. We phoned then to lodge a complaint they then asked us to put a broom on the mattress and take pictures and send them to them. Which we did. The feedback we got was that there is a stain on the mattress and the warranty is now a void. Our question was how does a stain cause a mattress to collapse...still no feedback. First of all the stain is very small. Second of all we will get the mattress cleaned......why do you say 5 year warranty then when there is a problem they turn there back. We will definitely not shop at the bed shop ever again and most definitely not refer anyone to them