I was charged for medical insurance that I did not sign up for.

I was wondering what I can do, Washington State University charged me for Medical Insurance, I called and they said that I "checked" the option for medical insurance when I registered for classes. I have never had medical insurance and did not check that option, I always deselect it. I talked to them and they said that the deadline for cancellation has already passed, they just sent me the insurance cards yesterday 10/23/09 and that sparked me to check my student account. Is there any way to dispute this when they already said, "sorry theirs nothing we can do."