Why didn't you go to the Apple Store? For a brand new device, if this happened, the natural way is to go to the Apple Store and return/exchange it. Even if it is out of warranty and even Apple refused to cover the battery problem for free, it's only about USD29 or so for changing the battery, and if the battery damaged the phone, I will insist them to repair it for free or at least at a really cheap price. Finding a random third party repairer for it doesn't seem to be a wise choice and I wonder why you chose this route.
[doublepost=1542449658][/doublepost]Anyway, in your case, I will return it for a new one. But also check the electricity infrastructure at your home to see if there is any unstable output from it.