ABSA debit my money without authorization

I need ABSA bank to respond to me ASAP and give me an explanation, when I call the call centre all the call centre agents keep transferring my call because they do not know how to do their job and provide me with the explanation that I want. on my bank statement I have noticed from last month there is a DR Unauthorize debit of R100 that is debited most of the time on the 2nd of every month on my cheque account, the last time I called the bank I was told this is an internal charge/debit by the bank, I want to know what is this charge? cause if ABSA can not explain to me I am leaving this bank.