Takes what ever is left in your account - when salary is not even paid yet

I have been with Capitec for quite a few years. My salary date is the 25th of each month. They get their loan debit order every month as soon as my salary gets paid in. I had R400 left in my account for petrol. Stop at the petrol station this morning, put in petrol, card gets declined. Logged into my bank account, see there is a debit order of R382.11 taken. I dont have a debit order of that amount. Phoned them, they say my loan is in arrears, so they took what was in the account. My salary will get paid in today. So who the hell gives them the right to just go into my account and take what ever they want. They have never had a problem with getting my repayments. I signed for a certain loan amount. Not whatever Capitec feels like taking from my account. I got refunded from work as well on the 18th, they also took the loan debit order on that date. I had to phone them and tell them to refund that money, as it is not my salary. My company told me my salary date is the 25th of each month, so that is what i work on. It is out of my control if my salary goes in on the 23, 24th of the month. They usually pay us early if the 25th falls on a weekend. SO CAPITEC - WHAT ARE YOU GOING TO DO ABOUT THIS INCOMPETENCE??????????