Can full time teach job be reduced to a part time job because I have asked for a position which would allow me to work with a small group of students?

I told my superintendent about my hearing loss and requested a position which would allow me to work with small groups of children. I've taught for 21 years, requested 2 years more in order to get 25 years in, (I purchased 3 years of service credit), and was told I had no job, just take disability. I then begged for at least something part-time. Was given a part-time position, lost my benefits, & salary was cut in half, but recently a new job posting for the same job was given to a retired teacher. I had missed to posting date, had spoken earlier with the principal about extending my hours, but was given no consideration for this job. Have filed a grievance but my education association is not supporting me the way I feel I should be. Had they discriminated against me 2 years ago? Should I push further and fight for what I feel was wrong? Thank you.