ActewAGL has confirmed 400 electricity, gas and water customers have received bundles of bills addressed to other utility customers in a massive privacy breach affecting 6000 customers in the ACT and NSW.
ActewAGL notified the Privacy Commissioner of the breach after it became aware of the mistake on Wednesday and had set up a taskforce by Friday afternoon to respond to affected customers.
The utility provider said it would work with its third-party mail house to investigate the issue.
Icon Water managing director Ray Hezkial said it was a logic programming error during the collation process that caused the mistake.
"We're aware that at least 152 customers have received such boxes with bills basically loose leaf in those boxes," he told 2CC radio on Friday.
Actew AGL general manager of retail Ayesha Razzaq said 248 ActewAGL customers had received invoices not intended for them, after the error affected three bill files processed between December 5 and December 7.
"We'll also be writing to all those customers as soon as possible to make them aware of the issue," she told ABC Radio Canberra.
By Friday afternoon, ActewAGL had collected 70 bundles.
The company said it would write to recipients it had not been able to contact by phone and supply a reply paid envelope to return the bills.
All affected customers would receive letters advising them of the mistake, an ActewAGL spokeswoman said.
Mr Hezkial and Ms Razzaq said the bills would be reissued, effectively extending the payment due date by 21 days from the new issue.
"We will reissue those invoices ... once we have confidence in our system and it’s back on track," Mr Hezkial said.
"We're taking it very seriously. Our priority is to retrieve those invoices and we've already started doing that."
Ms Razzaq said digital bills had not been affected in the privacy breach.
"I feel the buck stops with ActewAGL and I'm happy to own that," she said.
ActewAGL manages the billing mailout system for Icon Water.
The Canberra Times revealed nine cases on Thursday where customers received a cache of bills not addressed to them. In one case, a box containing more than 500 outstanding electricity bills was sent to a Belconnen address.
The bills appeared to be bundled by postcode, but some envelopes contained bills addressed to several postcodes in Canberra.
Bundles had been sent to addresses in Belconnen, Gungahlin, Chisholm, Calwell, Kingston, Palmerston and Waniassa, as well as a city post box.
John Steep received an envelope with about 150 outstanding gas bills on Wednesday and was told ActewAGL couldn't retrieve the bills on Thursday due safety concerns around driving in wet weather.
Mr Steep's bundle of bills was collected at 8.10am on Friday.
Other people who received the bundles of bills said ActewAGL did not seem concerned.
Larry Appley, who received 21 electricity bills in Palmerston, said he expected someone to ring back within 15 minutes after he alerted the utility provider.
"But I heard nothing," he said.
ActewAGL contacted Mr Appley after he posted a photo of the bills to the company's Facebook page on Thursday evening.
A spokeswoman for the Office of the Australian Information Commissioner said the office did not comment on specific reports.
The Australian Competition and Consumer Comission's Scamwatch website advises people to destroy any documents containing personal information because scammers can use information obtained through discarded documents, included utility bills, to commit identity theft.