By rejecting this, some have made shipwreck of their faith, among whom are Hymenaeus and Alexander, whom I have handed over to Satan that they may learn not to blaspheme.
1 Timothy 1:19-20, ESV
Imagine being Hymenaeus and Alexander. Did Apostle Paul go through the appropriate steps as in Matthew 18:15-17?
How lawless and sinful of Apostle Paul to do so. Where is the due process before Apostle Paul slams these guys for all eternity?
Sometimes you have to call a snake a snake, especially if you are first hand witness. There isn't always an opportunity to go through Matthew 18:15-17.
What if they refuse to talk to you?
I suppose in Apostle Paul's day, it would be even more impossible to "confront" many of these false teachers since modern communication wasn't readily available.