5SE first edition The mute button is on and won’t turn off.

[Mabelanne]

I can hear but my voice cannot be heard. With Apple Support I powered off twice, including the volume up the volume down quickly, side button held. This resulted in a black screen and after some seconds a tone sounded. No “Powering off” on screen. Nothing else. Mute is still off.
Overnight the 15.3 iOS update was installed. Powered off twice as before. Neither operation changed Mute status. My voice is still not heard. iPhone to Apple specialist.
This occurred immediately after phone conversation was played through onn. speaker via Bluetooth.

 

[J. A.]

Welcome to iPhone Forums!

First of all:
Apple Support tried to force start your device. If this is an iPhone 5 or iPhone SE (there is no iPhone 5SE), it works different:
Tap and hold Home and Power button at the same time until the Apple logo appears. As soon as you see it, let go of both buttons. Your device will power up on its own. Try it, maybe it’ll help.

The iPhone 5 series isn’t capable of running iOS 15.3, though, so I guess you own an iPhone SE.
You can see the correct model in Settings - General - About - Model Name, btw.