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@paula2404 You can ignore the display unit, it is not your bill. Just turn it off and do not use it. They often go wrong.
@whatacrock Ofgem rules are that power companies cannot reclaim debts more than 12 months old if the consumer was not told about them previously. If you were told the debt was building for a long time then SP are not allowed to go back in history to claim them. Look on the Ofgem website.
Read this from Ofgem.