Loan account still charging interest even though it was settled

I requested for a settlement quote in July 31st , then I paid up my loan but to my surprise they debited a certain amount of R276 end of August, and when checking again there is a balance growing on my loan which I settled on the 31st, I sent an email but till today no response , the account is supposed to be closed but not some interest is piling up even though I paid the full amount according to the settlement quote they provided.