Transparency is key

I have been banking with standard bank for as long as i can remember that is how much i trusted them. Firstly i took a sim card contract with them which the terms and conditions were not transparent although i asked and when i enquired when i saw a statement of R695 was told they will do an investigation to find out, waited and when i called back i was told the voice recording has been receieved and they will call back till today they had never done that and they have just been debiting, i kept quiet. Now on Monday 15th June my debits were returned because of a Saturday 13ths transaction now im liable for interest whose fault is that if the transaction reflected that it went through on a Saturday only for it to go through on a Monday? . Should i saw on a saturday that a transcation will only go on a Monday i would have known the status of transaction but my problem is that i receieved an sms for my purchace and the money left on my account, now why am i liable for interest? and when i called to enquire i was told to complain as im just liable. Anyway i know other banks are true reflections when the money is out it is out and yet for standard bank its usually just parked somewhere . Maybe its high time i consider a move.