My iPhone 4 screen is frozen

I can't exit my "phone" app just after making a call. My home button and off button are not responding. But my time and battery percentage are still working.

I tried removing SIM card- normal response

I tried plugging it in- started charging.

I'm not receiving messages and notification centre and control centre won't open. Unable reboot or reset it because my off button is unresponsive.

I don't have any apps from anywhere but iStore, my software is up to date, I have 1gig of space left.

Please help!