Billing on closed account

Good day,<br> <br> I received an SMS regarding my closed account with Altech Netstar saying the account is overdue and has been handed over for collection whereas I called the customer services requesting to cancel the account hence I sold the car. I do not understand how they hand my name over whereas I cancel the tracker with them. When I called the number in the SMS I was then told that the tracker is still active and I owe them R1039. I request Netstar to recall the handover and cancel this account.<br> <br> Regards<br> <br> Lulama Ntwanambi<br> ***