you situation is at will and being treated unfairly as you see it is a total nonstarter

I take it you are not yet " fired"

There is one big loose end in your post about being told there in no overtime ....that depends on details not in your post ...and in general CA has some very employee favorable rules as to how to count OT....so IF your employer is wrong as to OT you may be in for major recovery....but So far that's shooting in dark....some roles are not covered by OT and they,can work you til you drop.