The closest you get to "protestant" style Christian are the Waldensens, which began as a lay movement in the 12th century that got out of hand and rebelled against church teachings, but remained Christian as opposed to gnostic like the various Cathar groups, went underground because they were rejecting the sacraments, authority, and other things, that got them in trouble with the authorities, but before their time, you would be hard put to find any form of "primitive Christian" type groups. That is wishful thinking.
And those in the Catacombs were who?