Cheated by Sealy's complete lack of quality and integrity

We paid approximately R 5000 for a new Sealy mattress from the Sealy shop in Deco Park. This was approximately four months ago. The mattress sags so much, that my 81 year old mother, who weighs not much at all, rolls to that side every night during the night. The mattress was rotated, and the same problem. The store owner visited us at home, and insisted that nothing was wrong. A Sealy agent came out, gave us a case number, took photos, and we were told the next day that nothing is wrong with the mattress. On both sides there is just no support, it is as if there is a gaping hole in that section of the mattress. It has been one of the most disappointing experiences ever, and I decided to write when our housekeeper told me in no uncertain times that 'ouma had been cheated' - I am incredibly sorry that we assumed that a good brand will indefinitely remain good .... an old Sealy mattress that we still happen to have from approximately two decades ago, has far more firmness and support that this one with its gaping areas of nothingness in the middle of both sides ..... if this factory fault is normal, then Sealy should be prevented from conning the public by a body such as the Consumer Council or something similar .....