Which Christians are you talking about?
The term Christian is really ambiguous and may refer to multiple diverse cults who did not even believe in the Jesus story.
See Dialogue with Trypho and First Apology attributed to Justin
Dialogue with Trypho XXXV
First Apology XXVIAnd, 'Many false Christs and false apostles shall arise, and shall deceive many of the faithful.'
There are, therefore, and there were many, my friends, who, coming forward in the name of Jesus, taught both to speak and act impious and blasphemous things; and these are called by us after the name of the men from whom each doctrine and opinion had its origin.
For some in one way, others in another, teach to blaspheme the Maker of all things, and Christ, who was foretold by Him as coming, and the God of Abraham, and of Isaac, and of Jacob, with whom we have nothing in common, since we know them to be atheists, impious, unrighteous, and sinful, and confessors of Jesus in name only, instead of worshippers of Him.
Yet they style themselves Christians, just as certain among the Gentiles inscribe the name of God upon the works of their own hands, and partake in nefarious and impious rites.)
Some are called Marcians, and some Valentinians, and some Basilidians, and some Saturnilians, and others by other names.....
Based on the writings attributed to Justin there were people called Christians since the time of Claudiusc c41-54 CE but they were followers of Simon Magus.And, thirdly, because after Christ's ascension into heaven the devils put forward certain men who said that they themselves were gods............ There was a Samaritan, Simon, a native of the village called Gitto, who in the reign of Claudius Caesar, and in your royal city of Rome, did mighty acts of magic, by virtue of the art of the devils operating in him. He was considered a god........... And a man, Meander, also a Samaritan, of the town Capparetaea, a disciple of Simon, and inspired by devils, we know to have deceived many while he was in Antioch by his magical art. He persuaded those who adhered to him that they should never die........... And there is Marcion, a man of Pontus, who is even at this day alive, and teaching his disciples to believe in some other god greater than the Creator. ........ All who take their opinions from these men, are, as we before said, called Christians