Unauthorised Deduction, after payment arrangements

Good day,

I would like to find out how a bank has a right to go into my account and deduct funds without my authorisation or approval. To my surprise this morning, an amount of R2300 was deducted from my Capitec savings account instead of my standard bank cheque account where the payment usually goes off. I received a call on the 31st July and made payment arrangements requesting an extra R2000.00 to be deducted at the end of the month. Who gave Capitec to permission to go into my Capitec savings account and deduct money without my permission. Where on the contract does it permit your guys to perform such an ******* act. I would like the funds to be reversed asap. I dont think its acceptable that I've made payment arrangements and I view this as a breach of contract. I spoke to a very unhelpful consultant by the name of Takalani who couldnt assist but only gave me a bad attitude, no show of customer care whatsover. Please could someone contact me asap as I'm now in a predicament due this unforseen deduction.