The Lord Jesus warned all of us that He is sending us as sheep among wolves. Because of this it's a fact that we should not be surprised if we are treated wrongly or unjustly. It would be naïve of us to expect to be treated perfectly well, knowing that we are in a fallen world.
That said, we should not be discouraged from doing good to others. We should not shy away from treating others well, for fear that we might be treated badly in return. We must keep going on and doing good to others as much as we can.
Dear reader, it would be good for all of us Christians to come to the Lord whenever we are repaid evil for the good we have done. The Lord Jesus fully understands what we feel, and knows how to comfort and encourage us to go on. He went through so much more than any of us will ever go through, and knows how to comfort us.
To help you go through the pain of being repaid evil for the good that you've done and encourage you to keep going and doing good, here are a few Bible verses to comfort you.
Christ is our Model who went through undeserved pain - Hebrews 12:1-3
"Therefore we also, since we are surrounded by so great a cloud of witnesses, let us lay aside every weight, and the sin which so easily ensnares us, and let us run with endurance the race that is set before us, looking unto Jesus, the author and finisher of our faith, who for the joy that was set before Him endured the cross, despising the shame, and has sat down at the right hand of the throne of God. For consider Him who endured such hostility from sinners against Himself, lest you become weary and discouraged in your souls."
Christ is able to help us because He became like us - Hebrews 2:16-18
"For indeed He does not give aid to angels, but He does give aid to the seed of Abraham. Therefore, in all things He had to be made like His brethren, that He might be a merciful and faithful High Priest in things pertaining to God, to make propitiation for the sins of the people. For in that He Himself has suffered, being tempted, He is able to aid those who are tempted."
Christ sympathizes with us - Hebrews 4:14-16
"Seeing then that we have a great High Priest who has passed through the heavens, Jesus the Son of God, let us hold fast our confession. For we do not have a High Priest who cannot sympathize with our weaknesses, but was in all points tempted as we are, yet without sin. Let us therefore come boldly to the throne of grace, that we may obtain mercy and find grace to help in time of need."
