The main reason that you may receive slower than advertised speeds is due to your site's distance from the local exchange, which is a common factor when considering broadband speeds. Another factor that can affect speeds is the amount of users on the line at one time.
Contact us at support@ice-comms.co.uk or 0333 202 5000 option 1 for Customer Services then option 2 for Landline and Broadband and a member of the team will be happy to assist.