Plusnet has admitted that some customer accounts showed other people's names and addresses during a planned upgrade to its billing systems.
This was one of a few technical hitches the broadband pusher faced over the weekend, as both current and former customers reported being sent incorrect payment notifications, while a longer-than-expected downtime meant users were unable to access their accounts.
A spokeswoman for the company told The Register that it had identified a "handful" of accounts that showed "incorrect information", which included the wrong name and address.
Plusnet stressed that "full payment details were not visible" – but didn't offer any more specifics about what other users could see, or provide the exact number of affected accounts.
"We'd like to reassure all our customers that we immediately prevented access to the My Account section of the website and we quickly fixed the problem," she added.
"We take the protection of our customers' data extremely seriously, and have informed the relevant authorities."
Plusnet said that the move to the new billing system was "one of the biggest projects the company has undertaken in its 21 year history".
It had informed users there would be routine maintenance between 8pm on 31 August and 7am on 1 September – but systems still appeared to be struggling this morning.
Although the initial maintenance period is marked on Plusnet's status page as having been resolved, it was shortly followed by another "routine maintenance" alert.
"We're currently carrying out routine maintenance which means our advisors aren't able to deal with account specific queries and some of our web pages are unavailable. Thank you for your patience and understanding," it reads.
That was first issued at 4.54pm on 1 September and was updated with the same message at 5.03pm yesterday, although the "next update" was listed as 10am today (3 September).
Frustrated users took to Twitter to complain they couldn't access their accounts, while some current and former customers said they were being sent incorrect payment requests.
@plusnethelp Good morning,i have a message today saying i haven't paid my bill. I left plusnet & am now with sky,can you sort this out for me please.I have cancelled my dd as you gave advanced notice you were going to take money out so i stopped it,tia.— David Greaves (@greaves71) September 2, 2018
@plusnethelp what the hell is going on. Just had a text off you saying you've not received payment for my monthly service, but i pay by direct debit. Your systems seem to be frazzled at the moment and I cannot speak to anyone about this apparently.— Barry Roberts (@silentbazz) September 2, 2018
Another said her online account called for a payment of £43 – about half that of the amount requested by the firm in an email. However, Plusnet's customer support team was only able to apologise, as the maintenance prevented them from confirming account details.
Hi Rhianne,— Plusnet Help (@plusnethelp) September 2, 2018
I am really sorry that when signing into your online account you are seeing different information currently.
I do apologise but while the website maintenance is ongoing we would be unable to confirm these details with you.
For more inform... https://t.co/rSQZPPOyRd https://t.co/pI9I2o2vp9
The Plusnet spokeswoman confirmed that because of the maintenance, which was done as part of its billing engine migration, advisors weren't able to deal with specific queries.
"This also meant that some of our web pages were temporarily unavailable," she said. "We can confirm that work has now completed."
We've asked the Information Commissioner's Office to confirm it is aware of the issue. ®