Poor service

I bought Mercedes-Benz ml 500 diff with dry shaft for right back wheel, they ask for disc to give right parts. I was at venda in that moment I send my brother to buy for me , Mathew gave him wrong parts dry shaft is not for ml 500 car while he have disc that he asked for, when I return the wrong item they don't want to take them back.they said is no refund. Okay the other white guy said Mathew his not around he went to leave he will call me when he comes back ,even now I'm still waiting for the call from Mathew.service of this shop is very very bad. How can you sell wrong parts while you have disc of the car.