A forgiven person is a justified person. A justified person is a regenerated person. The slave in Matthew 18 had his forgiveness taken back. Jesus said this is like the kingdom of God.
This lord said this first,
Mat 18:25 But forasmuch as he had not to pay, his lord commanded him to
be sold, and his wife, and children, and all that he had, and payment to be made.
I think we need to be very careful when we interpret things that are taught. We need to know who the audience is for one. When Jesus taught the Jews He spoke to them using the Law of Moses. Very often He was teaching the intent of the Law, really was. Not how they had corrupted it.
Did Jesus mean to literally cut off an offending hand?
So when He says this is like the Kingdom of God does He mean that in the Kingdom of God your wife and your children will be sold? That they will pay for your sin?
Mat 18:34 And his lord was wroth, and
delivered him to the tormentors, till he should pay all that was due unto him.
Mat 18:35
So likewise shall my heavenly Father do also unto you, if ye from your hearts forgive not every one his brother their trespasses.
Where is the Kingdom of God? I believe it right here, in all believers, in the Church.
I believe that God is quite capable of sending the tormentors to teach us right here, right now. This may come from the Holy Spirit speaking of the righteousness of Christ and how we are to represent Him and His mercy. Bringing us to repentance and correcting what we have done or not done. This could be other Christians rebuking our behaviors. This could be that He causes you to fall into hard times and having your creditors demanding what you don't have.
I believe God is in the business of restoration through sanctification.