Weird brand new phone acting

Aight, so first of all, sorry for my poor English. Now, closer to the point.

Today i bought new iphone 7 32 gb and it was fine for a while. I've enabled it, typed my logins and that, then i put it on charge. After a while, when i came back to my phone, i wasn't able to unlock it (got that black screen with just a vibration on a home button). After rebooting my phone, while enabling it, i've noticed my screen had horizontal lines as if screen was broken or something. Lines disappeared as soon as home screen appeared. That was my first concern. I've checked IOS version and thought it might be an issue (it had like 11.4 version if i remember correctly). So i've tried to update through WI-FI to the latest one, but no success: during the progress of downloading or setting up an update, my phone could just reboot by itself with horizontal lines appearance: screen could be green, dark blue or grey with horizontal lines on it. And it all happened while enabling phone as i said before, so lines were disappearing as soon as home screen launched. I thought it was all due to an outdated IOS but then for some reason my phone just refused to update. Exactly the same happened when i've tried to update through Itunes. Well. Then i've made a soft reset of the settings... And somehow, after that, i was able to install a new IOS. Alright. Horizontal lines were present still and since i've updated IOS on my phone, now i have no idea will these lines appear again and what's the reason of their appearance and also my phone not being able to update and rebooting itself literally at every my attempt of updating it.

So my question is: what were the reasons behind all of that? Maybe i've got a faulty one and should ask for a swap? Help me and thanks for your attention!