Matthew 18:16-17

But if his heart is closed to you, then go to him again, taking one or two others with you. You’ll be fulfilling what the Scripture teaches when it says, ‘Every word may be verified by the testimony of two or three witnesses.’ And if he refuses to listen, then share the issue with the congregation in hopes of restoration. If he still refuses to respond, even to the church, then you must disregard him as though he were an outsider, on the same level as an unrepentant sinner.