I want to cancel my contract immediately

Disappointed with a new CellC contract signed on Friday evening 30 Nov.<br> The 64GB iPhone 6S Plus 'froze' after 3 days (Monday) (could not shut it down or use any functions). The manager insisted on sending the phone to their technicians for out of box fault investigation or something to that effect. I handed the phone to them yesterday early afternoon but have received nothing as proof, not even a reference number. <br> They were not able to book the phone in for repairs on their system due to serial number issues. They promised to send the request through by email and copy me in for my reference but I've received absolutely nothing...not even a courtesy phone call.<br> I signed up for an iPhone that proved to be defective. I do not want another iPhone or anything else from CellC. I don't want to be forced to take a Samsung phone of the same value instead, neither am I willing to take a hand-me-down \refurbished"iPhone 6S Plus"