Unisa - get your act together!

I have made a payment to register on January 25, 2020. The transaction was made, but Unisa claim that they haven't received my payment. It's so convenient that they have strikes going on. I cannot reach any of the provided numbers as all of them seem to be 'unavailable'. After various emails they still want me to make a payment of R5532 - which I already paid! This is unacceptable!