Rotten food

Went to woolies Norkem mall, bought the butter & cheese special. When I got home I realised that the cheese has mould on it, called the store was told to bring it back . Question who is responsible for paying for petrol money to drive back . Got to the store was given an exchange , the supervisor said we owe u , that was it . I want to know what does the policy say . I know Woolworths has different policies. Selling rotten food is a BIG No. putting it in a fridge that has meat in it is worse .