FNB debits outstanding debt without authorisation

I received an SMS for an amount of R4480 that has been deducted from my account. When I called the ***** department as my account is barely 6 month's old to complain that there is ***** in my account, I was told that this is forceful debit for my outstanding credit card from around 8 years ago and FNB is allowed to take anytime. I am so disappointed as I am now short to pay my accounts. I have been paying R500 every month without them even asking and still do this. This money was my groceries for the month. I have 3 kids including a 1 year old baby who I cannot feed this month thanks to FNB. I am not even safe to keep a bank account anymore and we should go back to keeping our money in the mattresses.