Is it slavery if people are working for almost free in prison because of some absurd crime and a bullshit justice system? Yes.

Therefore slavery still exists. It just got sneaky.

Well sort of sneaky - the English were calling their white slaves convicts. When people did crimes like steal bread, they could be sent all the way across the oceans on six month voyages to work. Yeah, they could eventually be free... but even if they managed that; then getting back was near impossible for most.