Unfair withdrawal of money from my account

Today the amount of R 4190 was withdrawn from my account and when I enquired I was told that it is for the student loan that I did for my sister. About two months ago I contacted the bank concerning this because my sister who is responsible for the account is on maternity leave and my personal banker told me to tell my sister to call credit department for arrangements because she will be going back to work in September. She called and she went to the branch in Polokwane and they let her call and arranged and was told that she will start paying off when she gets back from maternity in September and she must just let them know. Now standard Bank withdrawn double the amount of money she was paying, from my account without even arranging with me. It was better if they called me or wrote me a note saying how much and when are they going to be taking money from me. I have been banking with them for more than twenty years now and I have never missed any payment to them. How can such huge amount be withdrawn without my knowledge? I want the money to be refunded and the bank to make proper arrangement with me. I called the bank and got this two reference numbers ********** 375 and ********** 032. I'm just against the way the bank treated me after 20 years of being with them. They're treating me like a ***** or someone who is trying to get away with their money.

Please help me fix this.

Kindest regards Noko Victor Mashiane **********