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I'm sorry to hear about your situation. Assuming that you have documentation of a disability and proof of the training of this service animal (that is, it has to be a bona fide service animal) then they had an obligation to do this in both Federal and state law.
Establishments that sell or prepare food must allow service animals in public areas even if state or local health codes prohibit animals on the premises.
Because violations of Title II of the ADA are tied into the Rehabilitation Act, damages could be a possibility (42 U.S.C. § 12133) if a public entity is involved. If it is a place of public accommodation, injunctive relief and attorney fees are available (42 U.S.C. § 12188). The aggrieved individual may have remedies under state laws as well. In Texas, for example, wrongfully denying access to a person with a service animal is a misdemeanor punishable by a fine of not more than $300 and 30 hours of community service. Guessing wrong in Texas also results in the personnel being deemed to have deprived a person with a disability of his or her civil liberties, possibly giving this person a cause of action for damages with a conclusive presumption of damages in the amount of at least $300.
You can file an ADA complaint by going to this site and getting the form: http://www.ada.gov/filing_complaint.htm
As far as a state complaint goes, you can contact the police (on the non emergency line) and report the crime (again, it's a misdemeanor).
Hope that clears things up a bit. If you have any other questions, please let me know. If not, and you have not yet, please rate my answer AND press the "submit" button, if applicable. Please note that I don't get any credit for the time and effort that I spent on this answer unless and until you rate it positively (good or better). Thank you, ***** ***** luck to you!