Note 4 keeps shutting down randomly, and freezing?

I just bought this phone used off a good pal of mine, she was upgrading her phone plan to get the new iPhone and so happened my phone had broke recently and sold me her Note 4 for $200. We speak almost everyday, and she used her phone I guess a normal amount of time without any issues. I trust her and she s ensured me it s never once acted up with her. I ve now had the phone for a month, and for the past two weeks it s been giving me absolute HELL. Without much warning, while dialing a phone number, or checking Facebook the phone will freeze for a few moments then shut down. It would do this countless times a day. I did the obvious: checked for software updates, buy a new battery, restore the phone to factory settings, hard reset… I had my sis-in-law complete some sort of boot-up/update on my phone through her computer, and my phone has been working perfectly for the past 4 hours. And now, of course, it has gone back to being ****. I m wondering if there are any more steps I can preform on my phone before I have to call up my local phone repair man/Samsung and spend money. Thanks all!

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