Unisa is trying to make me pay school fees for a year I did not even register

If possible don’t go to Unisa! I was once a student at Unisa for 1 year in 2017. 2018 I had financial difficulties so I couldn’t register again for my second year. Since 2nd semester 2018 Unisa keeps saying I owe school fees. How can I owe school fees when I didn’t even pay registration fee for 2018. 2017 everything was paid. In my understanding and knowledge from past experiences, a person must pay a registration fee in order to be admitted fully. Without paying registration it means you can’t carry on with your studies. How then does Unisa say I’m owing 2018 fees where as I didn’t even register 2018. I even went to Unisa and they said “Are you sure you didn’t pay registration?” I asked them to show me the date of when I paid and the amount I paid for registration but they couldn’t do that. Almost every week I get calls from their lawyers and it’s annoying.