Hidden fee on Nedbank loan - they can't explain it

Quite disappointed and puzzled by the personal loans department at Nedbank. I have R2556 outstanding on my personal loan (for which I've been paying R3500 monthly) but when I go to settle loan option on the mobile app it suddenly adds R110 and I'm asked to settle by R2666. I asked the question on the Facebook page and they could not explain to me and gave me a number to call personal loans department which I did and the lady there (Msimang is her surname) she also could not explain to me why this is the case. I often incur charges including interest on the 1st day of the monyh and for October such fees have already been added onto the outstanding amount and I'm due for what should be a final debit payment in 5 days time which should be R2555. But if I settle now I'm charged a further R110 - why? Nedbank can't explain. R110 is not a lot of money but there must be clarity why it's being added.