I have just returned from holiday to be told that the smart meter has frozen & has been for a couple of weeks. thanks
The smart meter is the device physically connected to your incoming electrical supply.
What you’re talking about is the IHD, In Home Display. Press and hold the button on the back to turn it off and allow it to reboot. If that doesn’t respond, you’ll have to just turn off the power and let the battery run flat (about 1 hour).