Interest for fully paid loan

I took up a loan at FNB randburg branch. I finished paying the loan at the end of October and my balance was R0. on the 4th of November when I log in to online banking to my surprise I found out that they have added a monthly interest fee of R0.87 cents of which I don't know where it comes from because I finished paying that loan in October. No one told me when I was talking a loan that after it ended you still liable to pay monthly charges. To my knowledge I believe that as a customer I have to be given a full information for whatever I decide to take so that I can make rightful decisions. First it was a hidden monthly fee which was not explained to me because I was only told about interest fee, I went to the branch to enquire about that and the consultant explained to me very well how it works and I understood. now is this. If the loan has to be manually cancelled, I was supposed to be informed when talking up that loan because any instalment get cancelled after it has been fully paid. I'm very disappointed.