What should I do about a disagreement in pay?

I work at as a student secratary at my local college. I recently graduated and also moved departments. Upon my initial interview with the new department head I was told informally that I would be paid a higher rate that what I am right now. I have talked to the department head and they said that the initial higher pay rate I was told about was a mistake. I am just wondering what I should do.
1. Ask that I be paid the initial higher rate I was told about based on my increased education (I graduated this semester) and previous work for my college?
2. Work for a few more weeks and then resign?
3. Continue working?
4. Any other suggestions?
I am not greedy, but I just feel that I should not undervalue my self. Plus the new position that I am in requires more work and is more complex.

Lesson to learn, get all job offers in writing in the future.

If you feel you are being underpaid ask for a raise and look for a new job. Do not quit until you find a new job. You do not want to have to explain the break in work history in future job interviews.

Also remember to consider all aspects of your job not just the money when deciding to move.

Break some legs up in there! Just kidding! Odds are they are not going to give you the increase since they basically said no already. The rest is going to be up to you. Do you really like working there? Would it be to your benefit to stick it out and look for something else on the side but don't leave until you find it so you can get an excellent recommendation? If you just left would it be possible for you to get recommendations elsewhere? Also is there another higher up person you can go to with out breaking the "chain of command"? You could also work really diligently and prove you deserve a pay increase but it's basically all depends on your situation. Good luck hope you can figure it out!