Vodafone has issued a public apology after customers were left unable to use their phones abroad over the weekend - leaving many without service.
On Monday, the network said a "technical error has now been fixed", admitting devices were down outside of the UK on Sunday.
Others were wrongly sent bills in the thousands of pounds.
"We are very sorry that some customers could not use their phones yesterday, when roaming abroad," a statement said.
"This was due to a technical error, which we have now fixed.
"Some customers are receiving billing messages in error; we are working through these as an urgent priority and are removing errors from customer accounts."
Have you been affected by these Vodafone faults? Get in touch: emma.munbodh@mirror.co.uk
If you’re a Vodafone customer that's been affected by any of the two named issues, make sure you check your bill.
Find out if you've been charged for the right tariff, and whether the amount you’ve been billed is accurate.
If you think there’s something wrong then you need to challenge your mobile phone bill by reporting it to Vodafone.
However, the company has said that it's in the process of rectifying any issues already - stating customers do not need to get in touch on the back of the errors.
"Customers will not be charged and do not need to worry about contacting us as we are proactively checking accounts," the statement added.
You can contact Vodafone by either calling 191 for free from your Vodafone mobile or contacting it online.
Alternatively, you can open an online chat by clicking on the 'Pay monthly' button and choosing the 'Start Live Chat' option.
You'll need to enter your name and mobile number to get started. You'll also be able to print or save a copy of transcript using the icons at the top of the dialogue box.
Make sure you keep a record of all correspondence, including dates and the names of anyone you speak to.
If you're unhappy with the network's resolution, you can escalate it to the Ombudsman Services: Communications after eight weeks - or once you've had a formal response from Vodafone on your case.
Refund and compensation rights when a network goes down
When a network goes down, your provider is responsible for ensuring faults are fixed, and for keeping you informed of progress.
"In most cases, your provider should be able to establish reasonably quickly what has gone wrong and, if it is a network service issue, tell you how and when it will be fixed," Ofcom explains.
"Depending on the circumstances, it may be appropriate for your provider to offer you some money back while repairs are being carried out."
In more extreme cases, where repairs take much longer (for example it takes longer than usual to access a mast site to undertake repairs), you may be entitled to an additional refund or account credit.
This is to account for the inconvenience caused during the outage.
If you've been specifically left out of pocket by the technical error for any reason, such as having to pay for public wifi, you can complain to your provider and ask for compensation to cover any unexpected expenses.
Keep all evidence including receipts and emails for this as you will have to prove the expenses in your claim.
In cases where you have been without service for some time, you may also have the right to leave the contract without penalty," Ofcom adds.
There may be a term in your contract saying you can do this if your provider has failed in its obligations to you or breached a key condition.
If you've been sent an incorrect bill - and overcharged as a result - speak to the network immediately to get a refund.
This should take no more than three to five working days.
If you've incurred any financial losses as a result of Vodafone, such as overdraft fees or a direct debit payment bounced due to insufficient funds, keep evidence and claim this back from Vodafone.
Vodafone customers are paying for a service that rightly expect to receive.
If they don't deliver, you are also well within your rights to ask for the money back covering the hours affected.
This would most likely be your monthly bill divided by the month and multiplied by the number of hours affected. Vodafone will most likely have a threshold in place for pay-as-you-go customers.
I'm struggling to reach a resolution - what should I do?
If you raise a case with Vodafone, but you're unhappy with the outcome, you can submit your complaint to an independent Alternative Dispute Resolution (ADR) scheme after eight weeks.
If your problem cannot be resolved, ask your provider for a ‘deadlock’ letter so that you can refer your dispute to the relevant ADR scheme directly before the eight week mark.
Ofcom has approved two ADR schemes - CISAS and Ombudsman Services: Communications.
