Taking money from a pensioner

I am deeply disappointed in Standard Bank. My dad who gave me the advice to open up a standard bank account , had his all his life. After closing his loan account in 2005, 18 years later they debit his account taking almost half of his Sassa pension. Why all of a sudden. 18 years is a long time. If any qualified lawyer is reading this. Can they please tell me if this is Legal. I think this is disgusting.