Eligible to apply to a private school

In 2013 my daughter was enrolled in a private school. We got behind on her last payment for the year and then she fell off property. She is a cancer survivor and her bones were still very fragile. She fell off property and the school did not have an elevator to her classroom so I had to pay for extra tutor. In the meantime, I did not make the last payment and set up a payment arrangement with the school. I called the business office because I was 3 days late on payment and he told me he would not accept then a few months later they turned me over to a collection agency that kept sending me the letter addressed to my house but wrong name. I paid the bill. Now, my daughter wants to go back to the school but the school will not let us apply even though I paid them in full. They are denying her education right to apply to the school. She recently also got under the 504 disability plan.