CELL PHONE NOT FIXED / BAD SERVICE

I bought a phone at Game on the 15.05.2015 for 1 700.00 cash, which is still under warranty.On the 26.11.2015 I started experiencing problems with the battery and the screen went blank while I was chatting on whats app. However I could still receive calls and talk. On the 28/11/2015 I sent it for repairs. On the 6 I received an SMS from the store saying my phone is ready for collection. The next day I went to the store to collect it and the phone screen will not switch on,it vibrated once then stopped. I took it back 08/12/2015 and they said it must go back again for repairs for the second time before they can refund me which I did not get it right because its not written any where on the slip. On the slip is says that if its damage it will go for repaid and they will refund it if it is not fixed in 3 weeks. Counting from the first day it is almost 3 weeks, and again they had a chance to fix it and it was never fixed. The customer service manager promised to phone me back on the next day and she did not. I believe the the quickest way is to refund my cash or be given a new phone. I would like to have a new phone by Christmas.