FNB Revolving deducted 3x more than the approved instalment and have blocked me from excessing the funds

I app**** for a revolving loan at FNB Revolving Facility and I was given a quotation based on system calculation. The instalment seemed affordable however I had told the consultant that I would need to go check my financial status if I will be able to afford this instalment and the consultant(Annika) stated that if I end this call, I will not be approved for a better loan than this one that was offered so I took it based of the financial advise given to me by Annika. I asked her if the calculations were correct, consultant said yes and also stated that she had also confirmed the quote with her manager. The loan amount was paid within 48 hours and I settled some of the debts. Three days later I received a call from another consultant stating that there was a system glitch and the calculations on the approved loan was incorrect. I told the consultant for the fact that different departments approved it and still paid out the approved loan, it shouldn't be a fault on my end because on the day I was dealing with revolving loan consultant she(Annika) had confidently stated that the calculations of the instalment fee for the loan were in fact correct. I mean I do not work at FNB so I trusted her judgement. Please note that before funds are paid out, there is a process and different departments that it has to go through and my assumption was that clearly for it to be paid out, everything was correct. Due to an error on their end and my refusal to increase the instalment which if increased would mean I cannot afford even my child's school fees, they have deducted more money (3x time more) than what was agreed and approved upon. They have blocked me from excessing those funds which I desperately need or my debit orders will bounce. Revolving loan decided to take more money from my account without my consent instead of the instalment approved on the quotation. I sent a complaint to FNB but instead of dealing with my complaint, they just closed complaint without addressing the matter. From the 3x deduction made by FNB Revolving, my debit orders will bounce. I did not agree to any revised loan instalment but they still deducted anyway.