Daylight robbery

These guys are treating customers unfairly in that they don't accept returns no matter what if the part one asked for was "correctly'supplied.I recently brought a lower control arm instead of an upper control arm for my car.After I was alerted by my mechanic that I had bought the wrong one I tried to exchange the part for the correct one and they flatly refused.This was the very next day and the part had not been fitted meaning it was still in it's brand new state.I found this very unfair especially given that I just wanted to exchange and pay whatever price adjustment was required. They wanted me to buy the correct part and still retain the wrong one as a ploy to increase their revenue and the commission for the sale person concerned that. Is this even legal under the consumer protection act?