Having to pay for a broken phone

My wife upgrade her Vodacom contract on the 8th of November. Vodacom 4 U in Brits Mall gave her a new Samsung Galaxy S7. The phone froze, and we took it back on the 9th. The rebooted the phone in the shop, and gave it back to us. The phone froze again, and we took it back again, on the 10th. The Vodacom 4U in Brits Mall sends the phone in as a "out of the box failure". On the 18th of November the give us the same phone back, and says according to Vodacom, there is nothing wrong with the phone. The phone froze again on the 19th, and we took it back. We have not gotten the phone back. I went to the Vodacom 4U at Brits mall on behalf of my wife, to try and sort it out today on the 5th of December. They phoned the repair shop, and I insisted to speak to them directly, I spoke to Dess, who works at Vodacom repairs, she says that according to Vodacom, there is nothing wrong with the phone. The people working at Vodacom 4U in Brits Mall, agrees that the phone is broken, but there is nothing that they can do. It is now almost a month, since my wife took out this contract, and we still do not have a phone that works. this is absolutely ridicules. Vodacom sells you a broken phone, and expects you to pay for it every month for 2 years, and as long as they get their money every month, they are happy with the fact that you got a phone that you can not use!!!