Very bad services

So i opened an account for my son and there was R1500.00 in the account i than opened an account for my nephew at the same bank in brixton. To my knowledge these are 2 separate accounts and there should not be any problem if the one is in use it should not affect the other account am i right.But to my suprise i went to the bank today just to check my son's account and guess what there is a R1000.00 not there they have liked the account and my brother was using the other account and not aware that the money was coming of my account.so i asked the consultant how this is possible and he says that because it is under one profile which i dont see how that should affect my account .He told me i can open up a ***** case....really against my brother that didn't even know the accounts were linked.So who is at fault here and who is going to reimburse my mummy.Please tell me if im wrong but these 2 account should not be linked even though its under one persons name.I have 4 accounts with standard bank and have never had this problem....i am so frustrated with this bank now.