iphone 7 plus shut down

I have a iPhone 7 plus. Yesterday it shut down on its own. The screen went black and the phone was totally dead. I held down the on off button and the home button at the same time. I held them for 10 seconds or more several times. The phone wouldn't turn on. I also plugged in the phone to the lightening charger just to see if that would help. Upon plugging in the lightening charger it wouldn't even register that the phone was charging, it stayed dead and the screen was black with no indicator it was charging or plugged in. I let it sit for about a 1/2 hour then plugged in the lightening charger. It then registered that it was charging. I then did the sleep/wake home button and the phone turned on. I reset the phones settings. Later in the day the phone cut off a phone call I was using the ear plug for the call and wasn't touching any aspects of the phone to acciedently cut the phone call off. I needed a pass code to restart the phone call sign in. It kept telling me it was the wrong pass code. I know it wasn't, so I kept trying it. Finally I got through with the exact passcode it was previously denying. The phone cut off again and again the passcode was again registering wrong. I had friends call and sign in to check it. They could all sign in with the passcode, no issues at all. Only thing that makes since is the digits I was pushing on the phone dial screen were not being sent by the phone as the numbers I pushed. Any ideas or suggestions?