Everything about how Mysty voice treats you is on one screen: Settings → Account → Mysty voice, or go straight to /profile/mysty.

Turn Mysty voice off for yourself
The switch at the top stops voice for you and nobody else. It applies to the very next call, and turning it back on is one tap. If a lock is also in force (after a "This wasn't me", or after too many wrong codes) the screen says so and until when; that lock is not removed by this switch.
Your devices
Each phone or browser you enrolled is listed with when it was last used. Rename gives it a name you will recognise (up to 60 characters). Remove ends that device's ability to confirm a call, straight away.
Sessions and activity
Recent voice sessions show how each was confirmed and whether it is still active. The activity list shows what Mysty did on your calls and whether it worked, blocked or waited for approval.
If a call was not you
Press This wasn't me and confirm. Every enrolled device and every voice session is signed out at once, voice stays locked for 24 hours, and the workspace owner is told. You can enrol a device again after the lock ends.
For workspace owners
On Workspace settings you also choose which ways of confirming it is really the caller are allowed, and which roles may start a voice call. Keep at least one of each ticked; to stop all voice access, turn Mysty voice off for the workspace instead. A change applies to the next call, and the workspace activity list shows every call from everyone.