IPhone – How to switch off “hold home button” voice control

When the beep sounds you can ask:

"What song is this?"

It will speak the title, and artist. There isn't a way to turn this off sadly.

You say that your "display off button is numbed from excess use". Apple calls this the "Sleep/Wake Button"

One of the functions of the Sleep/Wake button is to power off the device. Another is to hard reset the device. A hard reset is performed by holding down the Sleep/Wake Button and the Home button until the device shuts off.

It seems likely based on what you've told me that the numbed Sleep/Wake Button has started intermittently being activated. This, along with a stuck Home button is probably activating the hard reset function.

I say this because you said that the voice control was starting on its own (stuck Home button) and that the "when the phone shut down, the rotating circle did not appear." This is exactly how a hard reset works.

This would also explain why you didn't see the 10% battery life warning and why, if the hard reset keeps getting activated, your phone wouldn't finish booting. You can activate the hard reset while the phone is in the process of booting.