Thousands of Pipex customers whose broadband service was switched when Tiscali bought a section of the company have been complaining about loss of connection and poor customer services.
A Tiscali spokesperson said that the customers were migrated without prior warning because internet service providers (ISPs) "do migrations all the time," the Register reports.
There are also reports that the company has refocused the ISP services it will provide to concentrate on customer volume rather than quality of service.
An outsourcing project has been a noted cause of controversy recently as Tiscali slashed hundreds of UK jobs in preparation for moving call centre operations overseas.
Offices in Stoke-on-Trent and Manchester are both due to close in the coming months.
Tiscali paid £210 million for the 570,000 customers affected by the move, hoping to solidify its position as a provider of lower-end broadband services.