University of Johannesburg stop ****ming your prospects

my little sister, app**** and got a space to study at the University of Johannesburg but she didn't get the accommodation, and we live in Durban so my sister deregistered Apon getting another offer that was better and had accommodation that was around march of 2021 when she accepted another offer from another institution she wrote a formal email and deregistered they took their sweet time to reply so now they are saying she owes the institution registration money, when she never even step into the institution and they say we saw your email later I swear UJ is a ****. they took the matter to the third party even on credit score she is in debt, and she is still a student studying this is emotional draining her.