MTN fails to honor their own contract. 2.2 clause

I upgraded my Package on the 06/08/14 and recieved a samsung Galaxy Grand Neo and within the 6 months warranty period has went to repairs more than 2 occasions and its for the same problem which the two first time it went it came with the same problem, they failed to replace the phone when we got to the third time having to return for the same problem and it has been by the repairs since the 5th of January up until now the 21st of February and I have not been assured of the situation and they do not want to replace the phone and I haven't been given a phone to use at least since the problem is on their side. I have requested for the phone to be replaced and contacted the Samsung personnel about the problem as well and the incident had a incident number of *** and the MTN reference number is ***. and i was told the Warranty covers the phone for an exchange for up to 6 months and now I have no resort but to ask for help here.