The JWs use the term "congregation" for "church," and it should be the latter. In latter parlance there were seven congregations that existed within the church, and these are the seven churches spoken of by John.
A paradox occurs in Acts 19:13-19:
Then certain of the vagabond Jews, exorcists, took upon them to call over them which had evil spirits the name of the Lord Jesus, saying, We adjure you by Jesus whom Paul preacheth. And there were seven sons of one Sceva, a Jew, and chief of the priests, which did so.
And the evil spirit answered and said, Jesus I know, and Paul I know; but who are ye? And the man in whom the evil spirit was leaped on them, and overcame them, and prevailed against them, so that they fled out of that house naked and wounded.
And this was known to all the Jews and Greeks also dwelling at Ephesus; and fear fell on them all, and the name of the Lord Jesus was magnified.
The people of the region saw that there was great power in the name of Jesus, but while some were justified in using Jesus' name, others were not. We don't know what motivated each group, but certainly motivation seems to be a factor. It may be the second group attempted to charge money, or attempted to use a priesthood they didn't legitimately have.
Still, it is a paradox.