If the screen is blank or showing a message such as ‘error’, ‘call help’ or ‘battery’, there’s probably a fault with the meter. Tell your supplier straight away or you could be left with no energy.
They must send someone out to repair or replace the meter within:
3 hours on a working day (Monday to Friday except bank holidays)
4 hours on a non-working day
The supplier doesn’t have to send someone out if they can fix the problem remotely - but they must do this within the same time.
If you need to top up your meter while you're waiting for your supplier, they should provide you with replacement tokens.
If your supplier doesn’t take appropriate action within the time they must pay you £30 compensation within 10 working days. If they don't pay you on time they have to pay an extra £30 for the delay.
https://www.citizensadvice.org.uk/consumer/energy/energy-supply/your-energy-meter/find-out-if-your-energy-meter-is-faulty/