Can I sue for being fired the day after I presented my employer with a letter demanding benefits?

I started a new job may 2010 and was eligible for health benefits according to the company plan after 90 days of employment. I started inquiring about it that august and continued to ask to be put on the plan on a weekly basis and nothing was done until i needed an emergency dental visit in december. at that time i was given the application and filled it out. a few days later i went to the dentist and was told that they called to verify my benefits and the insurance company told them i was not covered. i immediately called my HR person who assured me that i was covered and even called the dentist herself to explain that my paperwork was just being processed and would be completed the following week. i was also assured by HR that i was covered when i explained that i had a cobra payment due. based on the assurance of HR i cancelled my cobra and assumed i was covered. i came to find out in january that the application given to me by HR was for dental only and i was never given the medical form. once i found that out and demanded it i was given the form and filled it out. that was in february. the application sat on the desk of the HR person until April 11th. meantime, i did find out that when the HR person sent in my application for dental insurance in december she back dated the application to september and the insurance company had asked for proof that the premiums were paid from september which they were not and therefore the HR person could not provide them with that information and i was not covered/added to the plan.
while all of this was happening i was sending weekly emails asking about the status of my health/dental plan with no answer so on April 11th i presented a letter to the CEO and president of the company demanding that they either add me to the company plan or i was going to be forced to get a private plan and bill them for it. the next day i was told the company would like to "part ways" with me and terminated. i was not given a reason. i never had a review. was never on probation. was never spoken to about anything. and also, in my offer letter it clearly stated that medical benefits were part of my offer. do i have a case?