Man that is just patently ridiculous...Did the insurance company ever tell you the codes that you would need to have for them to accept the bill? The insurance company should know the codes they want from the documentation they received from your PCP. But if you have to find codes for them to bill (which is dumb) maybe these:
Varicella Titre - Z23.0 (Encounter for Immunization) or Z11.03 (Encounter for screening of other viral disease)
TB Test - Z11.1 (Encounter for screening of respiratory tuberculosis)
Hep B Titer - Z01.84 (Encounter for antibody response examination)
Don't know what to do with them though. Would you call your doctor to ask them to resubmit the claim with these codes? I guess keep in contact with your insurance company and PCP because 500 ain't no joke.
Another option for the titres, depending on where you live, if you really have to, you could just go to a lab and get it done (your insurance company may not have to cover it but you would still get the test). Companies like SonoraQuest in Arizona offer it (
Hepatitis B Immunity Screen (Hep B Titer Test) | My Lab ReQuest).
Mine was just through my PCP and while it was annoying, it wasn't anything like this. I know the email from the school sounds scary that "lacking immunizations could delay registration", but if you are making a good faith effort to get it done, no matter what happens you'll be alright