I helped my nephew to save up to buy a laptop at cash crusaders and he bought a second hand r3200 but after about 4 days the laptop had problems with the battery, it was freezing and was working extremely poorly

I helped my nephew to save up to buy a laptop at cash crusaders and he bought a second hand r3200 but after about 4 days the laptop had problems with the battery, it was freezing and was working extremely poorly. So he went back before the 7 days that was stipulated on the reciept adhere to when returning goods but was told they will repair and promised (cash crusaders) him that if it gives him problems again they would refund him. He took the laptop then after a few hours of use it died. He took it back and requested a refund now they are refusing to refund him or exchange the laptop with a working one. The managers name is Jane. Please help we need our refund back. He came home without the laptop