When Malcolm Loveland noticed his elderly mother-in-law's power bill was considerably higher than his own family's bill, he began to investigate.

When he discovered the bill had doubled three times in a row he knew something was very wrong.

"In March she paid a bill that when we saw it we thought was rather high," Mr Loveland told ABC Radio Adelaide's Mornings program.

"My mother-in-law is very elderly, lives in a one-bedroom flat and has no devices, computers or wi-fi or anything like that."

Mr Loveland said the 93-year-old had promptly paid all invoices.

"She read about high [electricity] prices and thought, 'well, that is what it is' and paid without question," he said.

So Mr Loveland called the provider, Simply Energy, and was advised the account was correct.

"[The operator's] advice was to call in an electrician to have everything checked."

After double-checking the bills, Mr Loveland again questioned the provider and this time was told a glitch had been identified in the system.

"They refunded over $400," he said.

Elderly at risk

Mr Loveland's mother-in-law recently received her latest electricity bill, and once again was charged more than double her usage.

When he called Simply Energy again he was told to disregard this bill and a corrected version would be issued.

"I try not to be too cynical, but there are two options here — it's either a glitch or it isn't a glitch," he said.

"If it's a glitch it is outrageous that it hasn't been fixed.

"I don't believe my mother-in-law would be the only one that have been paying double their usage."

Mr Loveland said he feared other elderly members of the community might be prone to not investigate bill increases.

"She is of that generation where they just pay up," he said.

"She is terrified of having her power cut off."

Simply Energy said it had a range of checks and processes to identify and address anomalies that appear on customers' invoices.

"We believe that this issue is unique to this customer and was caused by an administrative fault that has been rectified," a statement said.

"The customer has been refunded for any overcharging."