Bad quality furniture

In January 2018 we bought a lounge set at Lewis store Bloemfontein (St Andrew street). The lounge set was faulty : the armrest just collapsed as well as the sitting area. We struggled for more than 6 months to get the set replaced. After we logged a complaint at Head office the local store called and said we can go and get a new set. The new set was delivered at the end of November 2018. Not even within a months time the second set is falling apart. I want to know how I can cancel the contract because I cannot pay R 13 000 for a set that is falling apart. This is bad quality furniture that Lewis are selling so us. Lewis can send an assessor to evaluate the set at any time, we are not even sitting on the set anymore because we are afraid that it will fall apart.