Terrible service - cancellation

Cannot cancel our account. Sent written letter giving 30 days to cancel in August and it still isnt cancelled. We have called 20 times, re-emailed the letter about 10 times, each time the person you speak to says its being done, after 4 days we follow up and no-one knows anything. Same story every single time. Have asked to escalate to manager, have asked the manager and NOTHING happens.where are my rights to having something cancelled. We cannot get answers out of anyone. I have names and dates of all the people who have ****, saying its being done. No-one takes responsibility for their actions.