Faulty Skateboard Sold To Customer

Hi I bought my son a skateboard as a gift at Pick n pay Ottery Hyper I bought it a week ago,he enjoyed until a few days ago the child still playing and the ball bearings in the one wheel just gave in,I called the store the lady said if the board looked uses they can't change it,it's OBVIOUSLY used a child was playing with it.I mean I played R400 for the board a week ago now it's broken it's obviously a faulty board,I am a very good customer of Pick n pay,my son is very unhappy about his board.Please help me put a smile on my sons face again.Thank you MR Smith