Out of box failure

I upgraded on the 24th of July 2015. After receiving the phone I only managed to do a sim swap on the 31St of July 2015 so I can use my new phone. After inserting the new sim the phone showed no signal. Faulty phone. Took back phone today 1St of August 2015 and they tell me they need to send it for repairs..Why? It's out of the box never been used.. Should it not be replaced? Now I will have a brand new repaired phone.