Exchange query

I am so heartbroken of the service received from pick n pay greenstone today..as we speak I came to pick n pay to exchange the child’s formula of which it was incorrect the manager Thembi just told me that the formula can not be exchanged immediately it leave the store however the formula is still closed n it’s in the same packaging kodwa she refused to exchange it..I tried calling their complain and they said they can’t change Thembi the mananger’s rule which they just decided to create on their own.