Return Policy but not accepting returns

On Monday 9 April my brother bought a game for my son at BT Games Cape Gate as a treat, since they are visiting here from the Northern Cape. Last night my son wanted to play the game, and it did not want to work. This morning my brother took the game back to BT Games, as they have a 10 day return policy. Now the staff does not want to accept the game, since the disk is scratched and they are claiming we did that. The game was not opened in store when it was bought, and since my son only tried to play it last night, there is NO guarantee that we received a disk that was not already damaged. So how is BT Games going to assist us?