Contract Ended

my contract with Tracker ended on May 2015 and i called in to cancel the contract. now tracker call centre agents are calling me saying that the contract weas never cancelled and say that owe them money. the consaltant are so rude and when i demand that they have to check with their recorded calls to confirm my contract cancellation they say they dont have, now they are saying they are handing over my account to their artoneys. this is an unfair treatment as i have cancelled the contract, the problem is that their consultants are lazy to work hence they never update /take us serious when we call them. my reference number is ***