Cell phone send for repair

on the 1st of September I app**** for a cell phone upgrade at Highveld mall altech autopage store, my application was approved and I received a apple iPhone 6 plus, I included the new phone on my house hold insurance discovery, to my surprise the phone only worked for a week and suddenly stopped charging, I took it back to the store and it was send for repair under warranty, after a week I received a report from the store stating that the phone had a factory fault, it was deemed to be beyond repair, the store send a replacement, second hand phone with a deferent serial no, the replacement phone only worked for two days, lodged a claim they gave me a claim no, for the fist phone since it was insured, not the second phone, the insurance requested the first phone back for further assessment, altech repair Centre refused to hand over the first set to my insurance, they are forcing me to accept the second hand phone as a replacement whereas I bought and insured a brand new phone. I lunched a complain at the store and altech customer services and no one is willing to help, the reference no are 887447 and 899018, the name of the consultant at Highveld store is Brian Ngube