my iphone won't turn off - what do I do?

Depending on your iPhone model, use these instructions:--> Restart your iPhone, bearing in mind that you can use also the option to turn it off in Settings>General... then scroll down to the last option at the bottom (shut down).

Regards

Giulio

Then try a "forced" restart of your unidentified iPhone model:--> Force restart iPhone – Apple Support

Force restart your iPhone - Force restart iPhone - Apple Support (CA)