Cannot mute my ringtone since recent update, will go down to 1 bar and no further Any ideas please? I have to put it on do not disturb, which is less convenient than pressing the volume button.
This is usual behavior for iOS. The ringtone-volume can't be set to zero. If you want it muted, you'll have to use the mute-switch. 

Perhaps you're mistaking it with the volume for music, etc. (as soon as music is playing your side button will trigger 'volume' instead of 'ringer' - which can be set to 0).