Bank takes money but doesn't want to pay it back

Absa bank has been taking money from my fathers bank since 2013 without his authorization under the pretence that it was a loan. My father is 83 years old he hasn't had a loan in many years. the following amounts were taken 01/10/2013 R250, 19/12/14 R650, 19/11/14 R250, 18/11/14 R45, 09/03/2015 R865, 01/05/2015 R750. He changed his bank account number to try and prevent from even more money been taken but to no avail on 10/05/2015 R5200 and 19/07/15 R1165 was taken. He wrote them a letter with no response from them at all. He's been a loyal customer for many years and then this is how he is been treated. I want this fixed asap!!!