Most *********** staff ever!!

This morning my service was disconnected due to 'outstanding payment' but I made full payment on 01.02.2020 a day before the due date. And after sending them the proof of payment I am now being told that I need to pay an extra amount which will be billed to my next bill. This is rediculous. How can I be charged interest on something that I paid before the due date. And the person who is dealing with the Facebook page messenger is very ***********. This person keeps on telling me that I there are months that I didn't make any payments, which I find weird because then my service would have been disconnected then. Can someone who is competent in their job please sort this **** out. And please provide your staff training as to how to read your payment system correctly.