We understand your struggle and commend you for turning to God's word in your time of need. It's natural to feel bitter when faced with unfairness, but we must remember that God is always fair and just. As it is written in Psalm 18:30 WEB:
"As for God, his way is perfect. The word of Yahweh is tried. He is a shield to all those who take refuge in him."
It's encouraging that you're trying to find comfort in God's word and praise Him, even in your grief. The Bible tells us to rejoice always and give thanks in all circumstances (1 Thessalonians 5:16-18 WEB). It's important to remember that God looks at the heart (1 Samuel 16:7 WEB), and He knows your heart and your struggle.
When you find it hard to sing a new song or even praise God, remember that the Bible tells us that God inhabits the praises of his people (Psalm 22:3 WEB). Start with a willing spirit, and ask God to help you mean it from your heart. You do not need to give thanks for the unfair situation, but you can give thanks to God for who He is, for His love, and for His faithfulness.
As for the unfair deal at your workplace, remember that God sees all that is done in secret, and He will reward you openly (Matthew 6:6 WEB). Continue to work with integrity, knowing that your reward is with the Lord.
Let's pray:
Dear Heavenly Father,
Your word says there is power in the name of Jesus Christ, and it is the only name by which we can be saved. We come before You, Lord, lifting up our ### in need of Your comfort and strength. Help ### to sing a new song, even in the midst of grief and bitterness. Help ### to fix ### eyes on You and to trust in Your justice and fairness. Give ### the strength to continue to work with integrity, knowing that ### reward is with You, Lord. In Jesus' name, we pray. Amen.
Lastly, we gently remind you that the only way to salvation is through Jesus Christ. It is only by His name that we have access to God. If you have not already, consider accepting Jesus Christ as your Lord and Savior. As it is written in Romans 10:9-10, 13 WEB:
"because, if you will confess with your mouth that Jesus is Lord, and believe in your heart that God raised him from the dead, you will be saved. For with the heart, one believes resulting in righteousness; and with the mouth confession is made resulting in salvation... For, 'Whoever will call on the name of the Lord will be saved.'"
However, don't allow this sinful world of the current age make you bitter toward God. God hates deceit, and he says vengeance is his. God will reward you with eternal blessings for the unfairness now.