Vodafone says that a problem that knocked out broadband services for around 11,000 customers has been resolved.
The firm said it was “incredibly sorry” for the inconvenience caused after some people were unable to access the internet for much of the day.
It added that people should “already be seeing their connectivity return”.
It follows issues at Virgin Media O2 on Tuesday, when more than 50,000 broadband customers reported problems.
Vodafone told the BBC that Monday’s outage had impacted “just over 1%” of its 1.1 million home broadband customers.
Some users had expressed their frustration at the problems – which come at a time of significant price rises – with one calling it “shameful”.
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The firm is one of a number of broadband providers to have made large mid-contract price increases in April – with some customers experiencing rises of nearly 15% according to figures from price comparison service Uswitch.
Other users tweeted that the outage was affecting their ability to work from home, with one person asking if Vodafone plans to reimburse them for the cost of using mobile data so they can still work while the service is down.
Some accused Vodafone of failing to communicate with customers about the issues. “[Saying] ‘we’re investigating’ nearly 6 hours after a major outrage is unacceptable,” one user tweeted.
“I shouldn’t have to check Twitter and Downdetector [a site that monitors outages] to see what is going on,” another wrote.
Vodafone had said its mobile network was unaffected by the issues.
Rocio Concha, director of policy and advocacy, for Which? told the BBC too many customers of broadband firms were experiencing poor service.
She said the organisation’s research had found that “millions of customers aren’t receiving satisfactory service at a time when they’re also being hit by above-inflation price hikes.
“If you’re out of contract and not happy with your provider, now could be the time to switch,” Ms Concha suggested.
