I am sorry that you and your family and Godparents experienced this awful treatment on your birthday. I hope that writing and sending that letter will resolve the problem.
When I read about your experience, it reminded me of the Denny's discrimination lawsuit. Six African American Secret Service agents ordered food that took so long to arrive it resulted in them being denied service. There was a lawsuit which changed Denny's business practices and how they train their employees. If you feel up to it, you can send a copy of your letter to:
U.S. Department of Justice
Civil Rights Division
950 Pennsylvania Avenue, N.W.
Housing and Civil Enforcement Section, NWB
Washington, D.C. 20530
They handle discrimination cases at public accommodations like restaurants. If you are interested in filing a complaint, this
website can help. Wishing you the best.