Why notifications stopped popping up?

[AC Question]

Hi everyone,

I have had an Elephone P9000 (Android 6.0 Marshmallow) for two days and it had worked well until yesterday. The problem is that I suddenly stopped receiving notifications from Messenger, Facebook and Snapchat on my lockscreen, even though the option is ticked off in all the settings (internal app settings and general settings). Furthermore, even when the phone is unlocked, Messenger not always shows new messages**received. When I open the mentioned apps, I see all the new messages.

I tried to reset to factory settings. When I do it through Settings, the phone reboots but it does not go back to factory settings. I tried to do hard reset. The phone does not reposnd to the combination volume up and power button. However, it responded to the combination volume down and power,but it just enters factory mode, which includes auto test and some report, meaning that I am not offered the option to reset. First, it shows the elephone logo, then goes into factory mode. "An android logo" mentioned in manuals for hard reset of the phone never appears.

Is it a hardware problem/defect, or is it a system error (Android error)?

I appreciate your help