Blackberry selling damaged goods

I am really having a bad experience with MTN and Blackberry, this is the 3rd time I booked my blackberry Z10 for repairs in 2 months for the same problem, booked it in November 2014 and the phone only worked for just 1 week, booked it again in December and got it back in January 2015 and it only worked for just 13 days <br> <br> Now I recently booked it for the 3rd time since the 14th February 2015 and I was advised that the phone is waiting to be exchanged and that they waiting for stock since the 14th February 2015<br> <br> At the moment I had to borrow a phone for the mean time and when I call the MTN Helpdesk *** I am told that there is nothing they can do, all I have to do is just wait, i was told that I can even wait for 3 to 4 months before I could get a new phone.... Like really, is this fair...?<br>