Lost all notes I had saved on Notability (which my dad shared with me through family sharing)

My dad shared Notability with me about 2 years ago. Throughout this time I have a lot of saved notes, lectures, books, and documents. There were some issues with the credit card so I decided to leave the family sharing (note: notability was still functional after this and all my notes were there). Later I restarted my iPad and opening Notability would say "This app is no longer shared with you. To use it, you must buy it from the App Store". I decided to hop on back to the family sharing and was allowed to download the recent update for Notability. However the app won't open so I had to reinstall it. After the reinstall the app would open, but ALL of my old documents saved on Notability were wiped clean. I had turned off auto backup from the app itself so half of the notes were not saved on iCloud, however they were saved on the iPad, which was backed up on iCloud. In settings>iCloud>manage storage>Backups>My iPad, I could see Notability was there taking up 3.4GB memory so I assumed those were my old notes. So I erased my iPad and tried restoring with iCloud but there was problems with Notability restoring, and the problem still persists.

I would really appreciate some help in this situation as all of my university's work is on Notability.

Sorry for the lengthy read.

Thank you.