selling second hand faulty units as new one

At Sandton City today they sold me a second hand faulty massage chair cushion as a new one. We found the invoice of the previous owner whom returned it in the box. And it was marked for even less than what we paid for on his invoice. They then tried to give me another unit.... which was also second hand and not working. And refused to process my refund immediately as apparently only their headoffice can process refunds. That is unacceptable. ... now I have to trust a company that is not trustworthy to return my money tomorrow