OIA - good or bad experiences?

I am a final year student however i failed one of my exams and my appeal outcome was unsuccessful - they didn't accept my extenuating circumstance which was handed in after i discovered i failed - yep i know this is my own fault . I have an ongoing medical condition which the uni are well aware of. I feel like it was unfair the way they disregarded a legitimate medical note and was wondering whether going down the Office of Independent Adjudicator route would be a viable option.

My uni do offer another alternative to present relevant new material which would support my appeal - but i need good reason as to why it wasn't presented before.

What should i do?!!

Any advice?