O2 says it's fixed a 'network equipment' problem which left some users unable to make calls, send texts and access the internet on Monday evening. But if you've lost out financially as a result of the issue, complain and ask for a reimbursement.
Part of the mobile giant's network went down for seven hours, between 4.35pm and 11.35pm yesterday, leaving many unable to use their phones and tablets. It has not said how many of its 23 million customers were affected.
Customers of Giffgaff and Tesco Mobile, which piggyback off the O2 network, were also affected by the outage. See our Cheap Mobiles guide for help cutting costs if you're thinking of switching provider.
O2 says the issue wasn't location-based, and although it affected people up and down the country it appeared to be sporadic.
Can I get compensation?
O2 and Tesco Mobile both say they won't offer affected customers compensation, while Giffgaff says it is "looking into what needs to happen next".
However, if you incurred any costs, such as having to buy a paid-for wi-fi connection or use a paid-for phone service, keep records, complain to your provider and ask for reimbursement.
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If you didn't lose out financially but suffered inconvenience from the outage, again you can complain to your provider and ask for compensation. O2 says it will look into complaints on a case-by-case basis.
You can use our online complaints tool Resolver to make a complaint to your provider, or you can complain directly to O2, Giffgaff and Tesco Mobile via their respective customer services.
If your gripe goes unanswered for eight weeks or you get an unsatisfactory response, you can take your complaint to the free Ombudsman Services. See our How to Complain guide for more information and help on how to do this.
'Apologise for the inconvenience'
An O2 spokesperson says: "Yesterday evening some customers experienced a problem accessing our network and we apologise for the inconvenience caused to those customers who were affected. We restored service at 23.35.
"The problem was caused by some network equipment that was temporarily unable to correctly process mobile phone traffic for some of our customers. We have now isolated the problem to prevent this from happening again."
A spokesperson for Giffgaff says: "Our priority is to ensure that all members have a 100% satisfactory service, and now that has been re-established, we're looking into what needs to happen next. We'll continue to announce next steps to our community first, as always, so watch this space."