Customers are being "held captive" by Broadband services when they try and cancel or change their plans, the Citizens Advice Bureau said.
In the last year alone CAB received more than 3,300 complaints about internet and broadband problems. More than half of these related to sub-standard service.
CAB Chief Executive Gillian Guy said: "People are finding themselves held captive by bad broadband services.
"Internet service providers must not shackle customers seeking a better service with unreasonable fees that can turn into shock debt.
"All internet users need to be able to easily have a way out of inadequate contracts and broadband speeds that only give them daily frustration."
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