At what date did the “false” Catholic church begin? What happened to the original church?
It was a gradual process that was finalized when the first "heretic" was murdered in the name and by the presumed delegated authority of the Lord Jesus Christ.
The potentiation of it came about when Constantine made it the religious organ of the state politic, administered through one sole chief representative of an episcopacy granted the charter to rule over all churches and all their members with the presumed power to forgive or to withhold forgiveness for sins and therefore controlling soul life after physical death.
Remember, I said presumed Remember indulgences. Remember John's admonition:
"If a man say, I love God, and hateth his brother, he is a liar: for he that loveth not his brother whom he hath seen, how can he love God whom he hath not seen?" (1 Jn. 4:20 AV).
This non-negotiable rule has been abrogated by the RCC over and over and over again through persecution, torture, and fiery murder of their adversaries. They are therefore liars, are they not? And so is anyone who supports their dominion over a man's soul, eh?