Users of the network said they were not able to use their phones while abroad yesterday after being cut off. Meanwhile, they were sent messages telling them that they had bills of up to £11,000.
The company apologised, saying they had now fixed the error and were "proactively" checking accounts for problems. It added that customers would not be charged.
Twitter user David Maddison wrote to Vodafone's customers services team: "Been charged £5k for c200mb data in Malta last night. I’ve been here a week and used probably 10gig without a problem. Tried calling Vodafone this afternoon and after an hour my network has been cut off! So can’t even contact you. HELP."
Alison Wood added: "You got off lightly. Mine was £8000. It’s a computer error."
Vodafone said: "We are very sorry that some customers could not use their phones yesterday, when roaming abroad. 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 any errors from customer accounts. Customers will not be charged and do not need to worry about contacting us as we are proactively checking accounts."
Ru Bhikha, mobiles expert at uSwitch.com, said: “Vodafone customers who have been incorrectly charged for using their phone while abroad will be in for an absolute shock when their next bill arrives. The fact that this can still happen is incredibly disappointing and I would expect Ofcom to show a keen interest in how this is resolved.
“The onus has to be on mobile phone operators to proactively fix this for anyone who is out of pocket, and it is also important to acknowledge the knock-on effects this could have on their customers’ finances. If you are a Vodafone customer and think you’ve been incorrectly billed, check your statements to see whether the amount you’ve been charged matches what you’ve signed up for."