Defective mattress, customer not happy.

Bought a 3/4 bed on special at Pavillion through Matress king in Springfield park Durban. I had the bed for a few months and my mattress started to sag in and had it replaced whilst under warranty.

New mattress has now also sagged and due to the warranty being expiring, I have to now pay About R450 for A New warranty for a New mattress. They wanted me to pay this amount I understand the warranty is over but the mattress is defective from Sealy side and it's happened twice. I am not happy to pay for that amount to get a mattress that is not defective. It is a Sealy 3/4 bed king comfort firm. It is certainly not firm due to sagging. Your beds are faulty, and poor service delivery from Sealy. Mattress king in Springfield in Durban. is not helping us too. They need to make a decision on this as not happy. Thank you. Natalie