So how in the world are we to answer the OP if the mention of signs gets shot down by those who refuse to believe in them? The Pharisees did as much too...
The Pharisees accused Jesus of using diabolical power.
I'm not accusing anyone of using diabolical power; but there's no reason that a Christian ought to be expected to believe every claim of the miraculous; in particular when those claims of the miraculous are being used to justify positions which go against the Christian norm. There is no evidence that apostles were continually being called after the time of the early apostles, and the Church has always understood that apostolic authority and ministry has been retained, not in new apostles, but in the bishops and presbyters--pastors--called and ordained by the apostles to the shepherding and service of the churches. The apostolate served as the means for the spreading of the Gospel in the early ancient world and the establishment of the Church across the known world; we do not find mention of living apostles by the time we get to the sub-apostolic era; even the oldest among the fathers, those who sat at the feet of the apostles and given much honor for that fact, are not called apostle themselves, consider this statement from Irenaeus in the late 2nd century:
"
But Polycarp also was not only instructed by apostles, and conversed with many who had seen Christ, but was also, by apostles in Asia, appointed bishop of the Church in Smyrna, whom I also saw in my early youth, for he tarried [on earth] a very long time, and, when a very old man, gloriously and most nobly suffering martyrdom, departed this life, having always taught the things which he had learned from the apostles, and which the Church has handed down, and which alone are true. To these things all the Asiatic Churches testify, as do also those men who have succeeded Polycarp down to the present time,-a man who was of much greater weight, and a more stedfast witness of truth, than Valentinus, and Marcion, and the rest of the heretics" - St. Irenaeus, Against Heresies, Book 3, Ch. 3:4
Polycarp is first mentioned by Ignatius, in about 105 AD in both his letter to the Church in Smyrna as well as a personal letter to Polycarp; Ignatius himself being advanced in age and Polycarp relatively young at the time. Both men were taught as pupils under the apostles, and as such they present us with a vital link between the time of the apostles and the time after the apostles; and from them we see the rather clear establishment that the Church had been entrusted to the care of bishops and presbyters by the apostles themselves.
The chief claim of the "new apostles" usually boils down to a restorationist narrative, that we are living in "the end times" and so a "new outpouring of the Spirit" has come and God is calling up new apostles and prophets for the Church. That entire narrative has no basis in Christian teaching or Holy Scripture, and exists merely to facilitate those who would wish to be called apostles and prophets.
It ultimately boils down to something simple for me: Do I put my faith in modern so-called apostles and prophets, or do I put my faith in the historic witness of the Christian Church and in her Scriptures? The only sane answer I could possibly give to that is choosing the latter.
-CryptoLutheran