note edge shutting off will start back up if plug in why?

My Galaxy note edge will shut off any time it wants. Plug back in wait a few then turn back on. Talked to At&t said software problem, want me to spend 225 to replace even though not my fault, Talked to Samsung want me to pay 70 to have them look at it and not have my phone for over a week. I have a lot of medical problems. Help

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