If you don't manage to sort this out through normal channels I would take it as high within the university as you can.
I understand their rules, and you may well still lose, but you need to get this seen by somebody 'human' as it were, who has the power to bend the rules. If you have been averaging a first in your final year, the only year that would have counted, you clearly don't deserve to have an unclassified degree.
However, the first thing to do is speak to your tutor.