Be Broadband has fallen foul of the Advertising Standards Authority (ASA) after three people complained about the way its packages are advertised.
The broadband provider - which, along with O2's fixed internet offering, has been sold to Sky - has historically claimed to offer unlimited broadband, despite its deals being subject to a fair usage policy.
Under the terms of the policy, any customer using more than 150GB of data in a single calendar month, in an exchange with more than 80 per cent utilisation, would receive a warning.
The ASA revealed that 224 warning emails had been sent out to customers in the past 12 months, with the firm having around 68,000 subscribers.
Two customers switched broadband provider after being warned about contravening Be Broadband's fair usage policy.
In its ruling, the ASA said the claim unlimited broadband would be interpreted by readers to mean that they would be able to download and upload as much data as they liked, at any time without limit or penalty.
"We noted two users had left Be after being contacted about the fair usage policy and that a significant number had been warned to change their usage behaviour," the regulator stated.
"We therefore considered that, although it affected only a small proportion of customers, the service was restricted for those using more than 150GB in a month on some exchanges and was therefore not unlimited. As a result, we concluded that the claim unlimited was misleading."