In off mode, Mysa will not send power to your heater. The thermostat will still be on but will not turn your heaters on. This setting can be enabled manually on the thermostat itself or the Mysa app. Before you turn off your heaters, you need to ensure that if you have any shortcuts set, that they are set to 'hold until I decide to change' option. Lastly, make sure that you have disabled your geofence, to ensure Mysa does not turn on when geofence is activated.
Please also ensure that Mysa is either removed from smart home automation, or these automations are disabled. This will apply to Amazon Alexa, Google Home, HomeKit, IFTTT, and Samsung SmartThings.
On the thermostat: Hold down the down arrow until you see three dots on the display. Let go of the down arrow. The thermostat is now in off mode.
In the Mysa app: Tap the tile of the thermostat you'd like to turn off. Press the icon in the bottom left corner and a pop-up menu should appear. Tap off mode, represented by a plug.