FNB personal loan

I took out a personal loan over I think it was 60 months with FNB in the beginning of this year(January 2019). Within the fist couple of days I paid back 80% of the capital of the loan, but the loans interest over 60 months was not recalculated. I went to 2 branches that said it cannot be done and spoke to someone over the phone in an FNB branch who told me the same thing. I then emailed FNB loans and finally after about 2-3 weeks got my loan recalculated and the person who did it said it can be done. Everything worked out nicely I thought until I paid in R5000 towards my capital on the 20th of July, I sent an email to the same thread I did before to ask for a recalculation, Then 6 days later I sent an email again asking for help and nothing as if no one works at FNB loans. On 5 August I logged a complaint on FNB website since I haven't heard a thing. A lady phoned me from complaints on 6 August and apologised for the service and escalated the matter as she could also not get hold of the relevant department to have my loan updated. The thing is I still haven't heard anything and it's been almost a month. I have quite a bit of business with FNB, to think that the service is this poor for a well rated bank is well... mind blowing. Its not like me to usually complain but this makes me want to withdraw any/all business I have with FNB and go elsewhere.