Can’t shut off or do anything on phone

Press the low volume button, then the high volume button, and then press and hold the power button for RESET. Hold it until you see the white Apple

My apologies. It’s the volume up button then volume down.

• Press and quickly release VOLUME UP
• Press and quickly release VOLUME DOWN
• Hold the SIDE button until an Apple logo appears (15-30 seconds)

The operative word here is QUICKLY; and try it a couple of times, the timing is a little tricky.