Damaged iPhone given and refuse to exchange

I had upgraded my phone with Vodacom Fourways Mall, the repair centre by Wimpy to an iPhone 6 plus, later on in the evening I realized that the screen is cracked on the phone, I came back to the store today and they had blatantly refused to take the phone back despite the fact that the phone hadn't been damaged in my care and no one had gone through a check in store to ensure the phone wasn't damaged when given to me. Since then I have been given the royal run around with their customer car centre and the store itself placing the blame for their damaged goods on me. I have offered for them to inspect the phone, to look for other signs that the phone was dropped etc only for them to say that it must've been my fault, despite many reports available on the Internet about broken/ faulty iPhones. Very and extremely disappointed with Vodacom all I would like was for them to honor their exchange policy.