Mtn trying to ***** from the poor

I received a call last week from mtn claiming that I owe them an amount of R3020 which I dont understand because i cancelled their contract last year. Whereby I didnt receive their sim card again after I claimed from the insurance because I lost my cellphone but I was still paying insurance. I didnt continue with the contract but to my surprise last week they managed to call me to make arrangements to pay them why because they had a debit order running through my account why is it now that I need to pay something that didnt even try to go through my account and didnt get the money why would they try to ***** from us unaware of the situation no.