new device not working

The Samsung A5 was taken out on contract through MTN on 06/04/2015. In the second month of having the device, it started giving major problems ( half of the screen is black and phone is not accessible). In the third month the device stopped wotking completely. DOES NOT CHARGE OR SWITCHED ON ( never dropped the device, has no damage to it). Then went to Samsung branch in Brooklyn mall, after examining my device they said it is likely a factory fault and has to sent in for repairs and if it comes back that it is a factory fault a new device will be given to me. After going 4 weeks without a business phone, samsung brooklyn sent me a mail stating the device is repaired and ready for collection. On day 2 of having the device back, it was still giving the same problems as before. 1 month after the device got back from \repairs"it went back to completly not working"