Brand new broken Samsung S6 Edge

I recently received my upgrade from MTN, after being a client for 5 years +. The phone was delivered to my office, less than 1 month ago. Last week it went off without a flat battery warning, and now does not charge or turn on. I took this into the MTN store in Fourways, and dealt with a very rude consultant, who confirmed that he could in no way assist me as the phone is from a different department and i did not keep the box. His contract states under the terms and conditions that you need to keep the box for 6 months, mine does not. I left the store being told that i must phone them and sort it out myself. Surely, as an MTN store they should take responsibility for damaged goods? Horrified at the service received.