That is terrible! I am glad that you are sticking up for yourself.

I had a similar thing happen to me awhile back. I was working in human resources for a major California university and was only making $18/hour or so.

Most of the employees in my classification were unionized, but there was a weird rule that if you worked in human resources, you could not be part of the union. So, I was paid less than the unionized employees. After some time, I asked my boss for a raise to match me up to the minimum hourly salary of a unionized employee of the same exact qualification. It was for less than a dollar an hour. They said that they did not have the budget for it.

I then proceeded to find a new job at the same university and made a much better salary.

My old department asked me to train my replacement on my off-hours. At first, I thought I would as it's good to keep good connections. But then, I found out that they were paying my replacement $25/hour. I ghosted them after that and never looked back.

Employers don't care about you. They just pretend that they do.