Bad service by Rochester

I purchased slat bed cash with an amount of R7 500, including delivery and installation on the 24 April 2018 at Rochester Kolonnade Retail Park. However the driver, who delivered a bed, left a responsibility of installation with my son who was not aware that the driver should assemble and install the bed. I had to do installation with my son after work, where we realised that one of the plank is broken. I reported the matter to the shop on the same date, where I was promised that exchange will be done the following day 25.04.18. Until today 30.04.18 I am still sitting with a broken bed. Rochester does not want to replace a bed claiming that my son signed for it. My son did not purchase a bed, I did. I signed a contract with Rochester and not him. Therefore he does not know the agreement between me and Rochester. The very same driver who delivered a bed came on the 26th April to assess the damage. He informed my son that the plank probably broke from the factory. It was quick for them to take my money, for this bad service. What is process of getting a refund.