pounds 5000 bill shock for Margaret.
Scottish Gas claimed Margaret Meechan had worked her way through nearly 57,500 kilowatt hours of electricity in just 35 days.
Margaret, 59, said: "The first thing I did was turn off every appliance and run next door to my neighbour's house in a blind panic.
"But I knew I couldn't have used that much electricity. It wasn't Santa's grotto I was trying to light up."
Margaret, a retired shop worker, switched to a pre-pay card more than a year ago and shouldn't receive any bills from Scottish Gas.
She normally spends a round pounds 10 a week on electricity for her home in East Kilbride, Lanarkshire. Now she is waiting for an engineer to take a reading to prove she has been using her pre-payment key.
Energywatch Scotland said Scottish Gas should put her bill on hold immediately.
A Scottish Gas spokeswoman said: "We are sincerely sorry. We are looking into her case with a view to resolving this as soon as possible."