Sandra Lavender has been on a fixed low-rate contract with ActewAGL since having solar panels installed almost 10 years ago.

The family's contribution to the grid meant, until the recent installation of a new electricity meter at their home, they were usually in credit.

Ms Lavender contacted the company after receiving the quarterly bill on March 1, three months after the new meter was installed.

"I was advised the metering team were aware of the issue, and that my property was a one-off," she said.

After making a formal complaint with the promise of a response within 20 days, Ms Lavender used social media to gauge whether other households had been affected.

"We have just checked ours and realise the same thing has happened and we weren't aware," one Facebook user responded.

"Are you able to post this in Canberra Noticeboard as well? I think it is going to be a very common problem."

She did. The two posts found a handful of people who had also had their meters replaced and since ended up with big bills. Her posts helped them understand why it had occurred.

An error during the installation of the meter meant it was failing to register what was coming in from the home's inverter, despite the solar panels still feeding into the grid.

Ms Lavender said households on a lower feed-in tariff might be experiencing the same problem and continue paying a higher rate without knowing.

She said she'd used social media to connect with others in the hope more voices would send ActewAGL a message.

"You need to let people know what's going on. You need to let us know how you're fixing it," Ms Lavender said.

"They've just very much kept it quiet."

After commenting on the social media post on March 29, ActewAGL contacted Ms Lavender that day to provide an explanation.

The 20-day period for which they were required to respond to her formal complaint was up on Tuesday. She received a phone call from them that day.

An ActewAGL spokeswoman told The Canberra Times it had advised the metering provider of the fault when it became aware of it in December.

The spokeswoman said ActewAGL had anticipated the issue would be fixed by the metering provider prior to the next bill.

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ActewAGL said no other households had been identified as having the issue.

"This is an isolated issue and the result of human error which occurred during the meter installation by the third-party smart metering provider," the spokeswoman said.

"Unfortunately on this occasion, the bill was issued ahead of ActewAGL making contact with Ms Lavender.

"ActewAGL has taken additional actions to ensure that the same does not re-occur."

The spokeswoman said Ms Lavender had been advised her bill would be re-issued with the corrected meter data.

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