I purchased a used lg flex g2 and it will reboot at different times

[AC Question]

It is the LG-H950 has 5.1.1 and it is H95011x. I have done some reading up on it as much as I could understand.i am unable to do a hard reset. It won't do it. I did a soft reset with no change. I called at-t and they told me to call lg. Called lg and they said call at-t after I got aggressive they said I can send it in and they can look at it but it isn't under warranty any more. I got hostile and ended the call. If someone could please help I am willing to try anything. I just love the flex with my bad hands it is awesome to hold with little pain.