MTN MoMo Qwik Loan Settlement

I took out a MoMo loan. I had to settle a loan amount which was 2 days before the due date, which I did and still had money left in my MoMo account. Yesterday it said I didn't settle the amount and had to pay an extra R9.00, when I have proof of the transaction ID of the settlement. I don't understand how I owe R9.00 when it was settled before the due date and I still had funds left to settle any amount they wanted before the due date. This is the first time this has happened and I do not understand why this has happened.