Do sympathise about all this.
I have had much the same with other friends and in all cases HR were always on the company's side, I have learned that is their job and this is reinforced by our dottir who used to hire and fire for Tesco before lecturing in HR and other company law things at a uni!
Unions often have no clue, after all most of them have full time jobs and act unpaid anyway. And asking for help at work means people risk being "tainted" by helping you, in the management's eyes. So, sadly, human nature and all that.
I once started grievance procedure against a deputy head, only one person, my ex, said she would support me with evidence of her behaviour, although she was renowned for it. The day of the "hearing" she backed out too.
One of the most senior men in the NASUWT nationally came to the meeting but he basically just sat there and said little.
In the end it was something of a stalement but I got what I wanted and she got so frit she handled me with kid gloves until she resigned and moved on a few months later.
Other colleagues that the head basically wanted rid of, two of whom were union reps, got huge payouts to basically go away.
The whole situation is rank.
BUT if they have made mistakes then drive a coach and horses through them. This is what my missus did with dottir's help.
Very best of luck mate. No idea what game you are in or how badly you need to be employed. Can only sincerely wish you the very best of luck with it all.
PS, in Hull we used to call seagulls "sh1te hawks"