Utterly bad Customer service.

I bought a pain if jeans online. Wheni received the pair, it was exactly the same as a pair i already own. I took it to the Cresta store today to exchange and they refused as it was an online sale. Please tell why the f you can't exchange online purchases in store. It makes absolutely no logical sense? I work in luxury retail and this is such bad bad Customer service and totally unacceptable. I am absolutely revolted.