Charged for factory faults

I have purchased a Sealy Queen size bed from OK Gezina in December 2015. The bed is begining to sag. I am the only person that sleeps on this bed. The representative inspected the bed and found noisy springs however no explanation for the sag. So I must now pay R800 for the factory fault. I don't think so. I am being asked to pay for the matress to be replaced as if you add the cost of the mattress, the base and the mark up from OK then I am paying for another mattress at the factory price. i will not be taken for a ride. I will consult my attorney at your cost