Pope Pius XII's encyclical that mentions NFP is not de fide. It is not a part of the Extraordinary Magisterium, if it is contrary to what was taught then you must disobey it. From what I understand however, he states it to be only used in extraordinary circumstances. Do you have proof that it is contary to the faith in those circumstances? If not you are acting like a Protestant. In fact your whole contention here is ludicrous and schismatic. St. Pius X was the last great Pope but he was not the last Pope.
You like the rest of the Sede's have the same False obedience that the Neo-Cath's have. As St. Thomas says in the Summa, a Schismatic attitude leads to heresy through attempting to justify the schism.