My understanding of the hormone based birth control pill is that the egg is not released, therefore, no fertilization happens.
Your post seems to assume that the bc pill prevents implantation. There are devices that do that, but the bc pill doesn’t.
Usually that is the case, however, it does not fully stop that process. The second thing that bc pills do is prevent uterine lining, that would be receptive to a zygote (thus preventing what *should* be a pregnancy).