Unauthorised debit orders

The collections company that African bank hired to collect on its behalf is busy debiting my account without authorization. This is the reason I no longer pay my account. Wanted them to explain to me first who authorised them to debit my account as i had advised them that i have changed my banking details but they still go into my previous bank and take my child's school fees. To show that what they are doing is ***** they constantly change reference numbers so that when I dispute and block their reference they will be able to debut with a different reference. M sick and tired of this *****. Should it happen again I will be forced to report it to the police. In fact I am calling the Ombudsmen today. This is *******, want them to send me a recording authorising them to debit my account.