Watrant my foot

Went to the Vodacom shop to apply for a new contract, got the phone and everything. One day later found out that my iPhone doesn't charge. Now I don't have time to wait for repair which is like 5-7 working days according to them. So I remember them telling me that I can return it for a new one within 7 working days. So I want to exchange, they than take the phone out start rubbing and scratching the phone and then after a while they come back to me and say because they found a \scratch"it won't be exchange. I ask them to show me the scratch"