If I understand, your discipline has absolutely nothing to do with your allegations against your supervisor - those are entirely separate, were separately investigated and separately resolved. If your text messages or other evidence were not sufficient to convince others that sexual harassment or threats occurred, I'm sorry to hear that but you haven't demonstrated how that relates to the charge against you.

The charge you have described as having been made against you is "Unprofessional personal conduct and misuse of government property". That apparently relates to your shooting at the training session, and perhaps your response to the initial investigation. You haven't made that clear. However, you apparently have had representation through your union and, up to now, representation by a lawyer. You apparently now need to find a lawyer who is more familiar with the mediation process; it sounds like it would be sensible for you to pursue that option.

It might help if you were more clear about exactly what happened.