Unauthorized debits !!!

Their customer service are terrible ,I've been emailing, sending messages in their site and even whatsapp but no one ever get a back or no acknowledgment of your message but they quick to send you threatening mail or debit money from your account without your approval! I have been unemployed for years ,I sometimes get money sent to my fnb account (for food,kids or med bills) but not long after the money is in they would take a huge portion of my money leaving me with almost nothing .I have not authorized them to do that ,So can they and am I allowed to ask for my money back ? How do I take this further?