NSFAS Study Loan from 1999 - queried 19 YEARS LATER

I app**** for a study loan in 1999. I got married and started to work while studying. My husband and I wanted to buy a house in 2001, but then I was black listed to due this loan. I then went and paid cash at FNB, an amount of R2 404.00. The proof of payment was sent to NSFAS and my name was cleared at ITC and we could go ahead and buy the house. Now 19 years later I am getting statements and phone calls from them that I am owing them an amount of R4 297.08. I am again handed over to a collection agency. They want proof of payment again, how and where am I going to get it from now? 19 years later?