Broadband customers are being hit with cancellation fees of up to £625, the Citizens Advice Bureau has warned.
The consumer charity said consumers who challenge the fees soon found themselves in the hands of debt collectors.
Other customers became locked into a broadband service which did not meet their needs or were hit by excessive fees when they tried to switch providers.
One woman was hit by a cancellation fee, even though it was not in the terms and conditions of her contract, when she tried to switch provider after her broadband speed became so bad that she was paying repeatedly to use an internet cafe.
Citizens Advice chief executive Gillian Guy called on internet service providers (ISP) to "not shackle customers" and ditch cancellation fees altogether.