If you're paying too much for Broadband then ring the companies sales department. Let them know that you know you're paying too much and you will look to cancel, more often or not the ISP will already have cheaper packages available for you. ISP's are in a very competitive market...
Basically I would advise you to call your ISP to cancel and mention Sky are offering free broadband to TV package customers or BT are offering a free router, they will match it as close as they can, definetly request the free router.