Abnormally high phone bills often come out of the blue
Phone companies are being accused of not doing enough to monitor fraud on customers' accounts.
The problem is particularly severe for internet users.
In the past few months, 45,000 people have complained about rogue-dialler scams, in which the computer's normal internet access phone number is hi-jacked and diverted to a premium rate phone line.
Breakfast's Max Foster has been investigating.
We talked live to the Telecoms Ombudsman Elizabeth France
She told us that it's not enough just to bar calls to premium rate lines: you now have to protect yourself by barring international calls as well.
She added that traditional Telecoms companies like BT don't make much money out of these phone calls: they pass on around 98% if the profits straight to the premium or international phone lines.
Rogue diallers can insert themselves into a computer when you're using the internet, particularly through pop-up adverts.
They divert your computer from its normal Internet Service Provider to their own premium phone lines, often in remote parts of the world.
Gillian's computer was re-directed to Tuvalu
Many computer users don't notice what's happened, until they get an unusually high phone bill.
British Telecom and other phone companies have been refusing to reduce the bills of those affected.
Their argument is that the call has been made - and someone should foot the bill.
But a recent court case decided that BT should pay half of a £700 bill run up in a few weeks, because it failed to alert the customer to an abnormally high level of usage.
If you have a dispute over your internet phone bill, you can complain to:
Otelo The Office of the Telecommunications Ombudsman: 0845 050 1614
Icstis The independent Committee for the Supervision of Standards of Telephone Information services.
Cisas The Communications and Internet Services Adjudication Scheme: 020 7421 7444
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