Telkom debt collectors debiting my account without my permission

Debiting my account without my permission I want to complain about my account being handed over to debt collectors when I haven't even missed 3 payments. 2 of my payments returned but I went in to store and paid the cash in and they still debit my account with double the amount. The debt collectors have no permission to debt my account whenever they feel like. This is unacceptable. The fact that I have paid my account and the only bill outstanding is the current one which is due end of this month. So now I have the debt collectors debiting my account as well as the debt collectors. Is this even allowed?