The link below, from the Old Calendarist "Synod in Resistance", covers the problems related to the claim that the "New Calendar" was anathematized by Pan-Orthodox Councils. As others here have pointed out, only the Gregorian Paschalian was anathematized since this Paschalian contradicts the decision of an Ecumenical Council (the first). The Sigillion that you quote from (1583) is not an actual Sigillion from the 1583 Council, nor is there any reference to such a Sigillion being written. The so-called Sigillion from this Council that you quote is the creation of a Monk Iakovos of New Skete. He is the one who created (forged) this document, including the words "and the new calendar of the atheist astronomers of the Pope". Such a reference is not made anywhere in the documents which followed from this Council that are extant and authentic.
Also, while it is true that the days of the Revised Julian (New Calendar) do currently line up with those of the Gregorian calendar, the days are actualy calculated differently using the Revised Julian so they are not at all the same calendar. If you read the acts and decisions from the 1923 Congress (as unfortunate as this event was), those present make it very clear that in adopting a new calendar they would not adopt the Gregorian calendar because if they did so this fact would be exploited by Rome in order to proclaim Rome's superiority and convert more Orthodox to the Unia.
There is much to be admired among those who proclaim themselves to be "True Orthodox", but in proclaiming their "correctness" and departing into schism, they have still cut themselves off from Christ. Elder Eprhaim of Arizona, who you criticize for being on the New Calendar, was once an Old Calendar schismatic and saw the error of these ways. Elders Joseph the Hesychast and Ephraim of Katounakia were likewise once schismatics but it was revealed to them by God that the schismatics are separated from the Church. The same was revealed to Elder Cleopa of Romania and countless other contemporary saints.
To find out where the true Church is, see who continues to produce saints just like those of old, and see who only produces false zeal and endless schisms.