Hi Lolly,
My thoughts are you should submit a new claim ASAP because the sooner you submit, if it is awarded it will be backdated to the date you made the claim.
If you want to separately challenge the original decision you could try to do that once you have put in the new claim.
I wish you luck with both but frankly I don’t hold out much hope for challenging the original decision.
Regards
Pete
Nothing on this board constitutes legal advice - always consult a professional about specific problems