Robbery at brought day light

My brother who is a 1st year student at NMU in PE bought a laptop at Cash Crusaders at R4900 Friday the 1st of April, and sent it back the next day,because it wasn't satisfactory to him, it also made a strange noise and it was popping a message that there was a virus on it, they refused to take it back saying he must sell it to them for R3500, that's a rip off considering he bought it for R4900.