Telkom cancelation or ***** taking place???

We have been trying to cancel Telkom since May 2019, everytime we phone they say it is canceled, yet we still receive an account every month now going into a minus saying that they owe us, but this is impossible as we have never over paid the account. So my question is, is this ***** that is taking place on their part? Or just plain right a mistake in their part, I don't know, but this issue needs to be resolved. My father is a pensioner and he is worried he will be implicated in something that telkom is doing, this is why this account needs to be closed and there should be no money owed to him. Can anyone help?