Best phone ever ! its the last one with a single messaging hub which is something I really use every day - hate opening all the apps that notify me when I don’t want to. True they dont support it any longer but at maybe 100$ now you cant beat it. I use it until it breaks and then use one of my spares :D Samsung is just catching up to the screen design and Google pixel 3 aint even close yet.
while off and after say giving it 10 minutes to charge plugged in and leave it plugged in - try holding down the power button and the volume down button for about 10 secs together at same time. Release both at same time and wait 3-5 seconds the screen should show a hard reboot screen in weird DOS green fonts - select the continue with reboot up one and it will start up again - happens to me a lot and I am still using it! Best Phone EVER!