Money Taken!!!!

I have a cheque account with Standard Bank as well as a Business cheque account. On the 27th of February Standard Bank took R3500 from my savings account. I did not make arrangements for any amount to be deducted from my account. This is not the first time that this has happened, when I called the call centre they just tell you to go to the branch. The consultants in the branch just pacify customers by telling them that they will investigate or that the funds will be put back into my account within 30days. I still dont have a real explanation as too why funds are being taken from my Account How can money just get taken from your account by an Institution which is supposed safe guard it and with no consideration of my personal obligations!!!!