PLEASE CANCEL THIS ASAP

I have been with cartrack for 3 years and I am legible to cancel at any time because I reached 3 years contract with them,now when I call them today to say they must cancel it as I no longer need it and one of the reasons I'm cancelling is their bad reputaion and poor service now the agent say I must pay again at the end of the month,Why??? Where i notified you guys 27 days before the following debit order goes off again ,,Please stop being ****mers.