I have a work-related legal question?

I've worked at a company for over 5 years. Last year, I was told that I was promoted to supervisor of my department. I was then told that after 6 months of proving myself efficient, my performance would be reviewed and, if all was well, I would get the monetary raise that came with the new position. After 6 months, I was told that I've been doing fantastic but I would have to wait a few more months until the raise could be discussed. After that few months went by, I was told the same thing. It has now been a year and I brought the issue up to my manager. He then told me verbally that I was never promoted to supervisor, hence I will not be getting the raise. The problem is that I have been doing all of the supervisory work for that year, and then some. I still have the email which clearly states that I was in fact promoted to supervisor from my manager on the date I was 'promoted'. Do I have any grounds to take legal action for retro pay? How should I handle this?