FNB BANK- HOW can we not help you!!

I took out a personal loan with FNB IN April 2016 and have been paying them every month with no issues as this payment was debited from my account. So in June 2018 I was surprised that they did not collect their installment as per usual, I then decided to call FNB and find out what was going on. After being told to hold the line for close to 45 min, I was told that my account was in errors and that my debit order date has been changed hence why the June installment did not go off. I then asked who authorized for my debit order date to be changed, they could not give me an answer all they could say was that I need to pay the errors as this will reflect badly on my credit record. WHAT THE HELL- so much for "FNB, how can we help you". Can they not go onto their system and see WHO changed my debit order dates- according to me FNB always shows off that they are so advanced technologically but yet a simple thing as picking up who on their side went into their system & CHANGED MY DEBIT ORDER DATE, without notifying me... I asked to speak to the collections department supervisor because the consultants I was speaking to had no answers for me , the only thing they could tell me was that I'm in errors (due to THEIR negligence and incompetence). The supervisor I spoke to also had no answers as to who and why my debit order dates where changed. Now they are forcing me to pay extra on my installment for the mess they caused, but they are unable to give me answers. I've been a loyal client of FNB for so many years, but after my experience today I will not think twice about changing banks........ So much for "FNB, how can we help you" should change to 'HOW CAN WE NOT HELP YOU' mxm!!!!!!!!!!!!!