Poor quality bed that plunges in 1 month of purchase and refusal to exchange their poor quality product

I bought a medi-spine Queen bed at UFO furniture Tzaneen branch Limpopo,the whole mattress is plunging within first month of purchasing it,I lodged a complaint and UFO branch manager came and checked the bed and accepted that it’s indeed plunging,He lodged a complaint to their supplier Viva bedding for faulty base set and the supplier which is Viva refused to exchange the bed because it was having a small stain that was not evn at the middle of the bed saying that 1cm stain is the one that caused the whole matress to plunge.I am highly dissatisfied in their poor quality hence expensive bed.This is day light ******* and need to be investigated.