its not illegal. Anyhow the consumer can petition it saying they didn't provide quality of service, Even through you may have not signed up for a 40GB limited service, it depends on the QOS. You can definitely go against SLT, as few months ago it was even published on the Sunday Times where SLT declined and said they cannot offer such services as for such a growing market. What you can do is tho if a large number of people say they have been violated and had been fraud-ed by a huge corporation like SLT, then its within the organization to provide assistance at least, as because it is unfair to a huge number of people and this is stated in the law that if a large number of people have been found that any company had violated there terms as a principle can take action if they all handed proper complaints and regulated them with the proper authorities.