phone repair

I bought Samsung galaxy s6 edge for R15000 it was faulty , I send it back n they booked it for OBF. They returned it , it does the same thing . Then they send it back to the supplier . It almost three weeks now they haven't given me my phone and I bought it cash. I told them I need my money back they say it's not possible. I only used the device for only three days. Please help . I want my money back. Or a new device.