Incredible (refusal of refund) Connection

Sales people are quick to sell you goods but when ink cartridges are not compatible with a printer then they refuse to issue store credit or a refund (despite not being able to refer to any provisions in their terms and conditions) on the grounds that the returned product would not be able to be sold by them. After spending thousands and thousands of rands at the store not a week ago, the manager turns up to tell me I cannot be refunded a couple of hundred of rands for cartridges. This franchise is in Cavendish Square in Claremont.