Poor service

Upon trying to exchange an unopened bag of dry dog food i was informed by the manager at the Cape Gate branch that they only accept exchanges within 7days (this is not printed on the slip) as they can't confirm how the dogfood was stored. When I stated that the bag was still sealed, the manager told me it is the law and that I should go read the law. I then questioned how come supermarkets accept returns on unopened perishable food stuff, and again the reply was to go read the law. Pathetically poor service with unknowledgeable staff. Exchange/refund policy could just as well be non-existent, which is in obvious contradiction to the consumer protection act.