Christians were call atheists by the Romans for not worshipping their gods.

No no, their thinking was rather like this: if there is only one God, then this God is a poor guy, almost a slave.
Quotation needed? Here goes:

"The immortality of the gods must be
worshipped by all, and their plurality feared
everywhere. They are stupid and truly foolish
who say there is a single God, and impudently
speak against the rites of old. For if we believe
there to be a single one, who presides over
everything, we grant that this [one] is subject
in contradictory ways to different [powers],
since on the one hand he nurses the good of
peace with clement mercy, [and] on the other
hand arouses the tumults of war with savage
cruelty. Thus there are many and different
offices of the gods, which are a sign to us of
the difference between them. Therefore those
who say that a single one presides over such
different matters – their god is inevitably
influenced by contrary powers."

In Latin:
"Deorum immortalitas
est omnibus colenda,
eorum et pluralitas
ubique metuenda.
Stulti sunt, et vere fatui,
qui Deum unum dicunt
et antiquitatis ritui
proterve contradicunt.
Si enim unum credimus,
qui praesit universis,
subjectum hunc concedimus
contrarie diversis,
cum hinc bonum pacis foveat
clementi pietate,
hinc belli tumultus moveat
saeva crudelitate."