Unfortunately you do fall foul of the ELQ ("Equivalent or Lower Qualificaton") rule, which states that you cannot get Student Finance funding for a qualification which is lower than, or equivalent to, a qualification which you already hold.
It's a well-established SF rule so I'm not sure what grounds you might have for appeal, unless SF gave you incorrect advice and you can prove that. Ignorance of the rule is unlikely to be accepted as grounds for appeal.
I do feel for you. I hope you manage to sort something out but I'm not optimistic based on what you've told us.
Could you explore the option of doing a PGCE in order to get into teaching? Might be a longshot without the degee, but you do at least have a postgraduate-level qualification and PGCE funding is separate to other funding so I don't think your PGDip will count against you on that score. Do check that direct with SF though.