Employer invalidating diagnosis

Hi, My employer seem to be invalidating my AS diagnosis. I had a disciplinary appeal the other day and somebody made the comment' Oh that's just one person's opinion', I was gobsmacked all the problems I have had throughout my life and it was like this one person brought my whole world crashing down. I have struggled all my life with communicating with others and feeling different, I got my diagnosis 3 years ago from a psychologist that advertises on this very web site, who specialises in adult AS diagnosis and used NICE guidelines, surely that is proof that this person is is qualified to diagnose AS, isn't it?