Hello, thank you for your question.
My name isXXXXX can answer this for you.
What would you like to know specifically please?
If you are out of time, you are unlikely to be able to get it heard now except for a very good reason. If the reason is Unison forgot to lodge it, then that's not a good reason.
You would need to sue unison for negligence.
You say they admit negligence, so now it should be a case of them paying out if you had a good case.
You need to get a solicitor involved, who can sue Unison for you.
You cannot expect Unison to help you if they are a potential defendant and potentially in the wrong here.
You should be able to get a solicitor to do this on a no win no fee agreement for you.
Strangely, from the perspective of legal costs, you are likely now to be in a better position that you were beforehand when making the complaint yourself to the employment tribunal.