Utter dissatisfaction and disappointment with FNB Customer service

I am so disappointed and dissatisfied with FNB. I have a loan I took in 2018, now am left with one month to pay up. All of a sudden I saw R850 added to the debit which appears as arrears. I have not skipped any payments, instead I paid in R1000 in October last which would make my last instalment less. I queried this via their secure chat where I was taken from pillar to post. I was transferred to more than 5 departments which is time consuming . The last consultant I communicated with told me they had escalated the issue to the loan admin and would get back to me after 24 hours. I waited for the whole week and no one came back to me. I initiated the issue again via the secure chat and no one assisted, this time I was told your issue has been escalated and there is no timeline. I called the private banker(I don’t even know if there is anyone who gets value out of these so called bankers). I got an email stating that I would get a response within 48 hours. I stayed for the whole week again with no feedback. I wrote an email to the banker and analyst who them responded with a crazy answer that I missed an instalment in 2018 around the period of September and December. My question to them is , for 6 years the system could not pick up the so called missed instalment, secondly if there was a missed instalment why was my debit going down steadily as per the repayments , why didn’t the so called missed instalment kept my debit high, if I had missed an instalment why is the so called arrear is way less than my monthly instalments, it is not even half of my monthly instalments. FNB clean up your house, there is serious problems there. I checked my statements and were all corresponding to what I was paying except this R850 that they decided to add to my account this month. Be careful of these guys. R850 seems to be a small amount but how many R850s are being looted from different people. After paying very heavy abnormal interest , one gets to be ****** more. I am so disappointed with FNB, a bank I have been with for more than 16 years