IPhonenot working 3 weeks after getting it

Hillcrest Cell C has to be the worst in the history of customer service. My daughter got a new IPhone 6 20 days ago and yesterday it started giving problems. I took it into the Hillcrest branch and was told it will have to go for repairs which will take 21 days. I object to this as NO phone should stop working after 20 days and why should I then have to pay for those 21 days which it will take for them to look at it. I asked Monica the \manager"to call as I wanted to speak to a senior manager. I had to wait another 10 min as they only have one phone to call head office"