Is there something I can do if my 90 day evaluation is disregarded?

I signed into a car dealership company four months ago now. I was promised after 30 days that I would get a raise from $10 to $12. After I waited that month, I went to them and they said that it was moved to be a 90 day evaluation because I got a different position than what I applied for. So, exactly on my 90 days, I asked my manager again, she told me go ask the general manager. I went to the general manager and even the store manager. They said wait out the rest of the month and then ask them when they aren't busy. I am also 6 months pregnant with twins. Yes, it is in writing and I signed it saying I want to receive my 90 day review. I was relying on that raise to help me pay my bills while on maternity leave.