altech vener cancelled my contract as i requested

i had a tracker with altech ,in july 2014 i requested to cancellmy agreement and i was told it will only expire in september 2014 and i can only cancell it by then. in sept 2014 i called to cancell and a consultant informed me it will be cancelled . i was surprised 2 months ago to receive a call from debt collectors Nu debt ,i told them the story,but i keep on receiving irritating calls . i am not going to pay money for something i made clear that i dont want.