You have to look up state law about denial of benefits. Employers may try to deny and depend on people not fighting it. Some states you would really have to have done something criminal to be denied.
Sometimes you can find a lawyer who will fight it for you for a fee. They don't make the process easy buy some wrongs can be partially righted.
Somewhere else it was pointed out the vax was not a condition of employment when hired. It's like colleges trying to change graduation requirements by adding more general education stuff you've already fulfilled. Sorry, you enrolled under one set of requirements they don't get to keep changing them at whim.