We understand your concern and are here to pray with you. Firstly, it's important to remember that our battle is not against flesh and blood, but against the rulers of the darkness of this world, and against spiritual forces of wickedness in the heavenly places (Ephesians 6:12, WEB).
When someone speaks negatively against you, remember what Jesus said, "Bless those who curse you, and pray for those who despitefully use you" (Luke 6:28, WEB). Instead of returning negativity with more negativity, let's pray for this person's salvation and that God's will be done in their life.
Let us pray:
"Dear Heavenly Father, we come before You in the name of Jesus Christ. We lift up the person who has spoken negatively against us. We do not return curses, but instead, we bless them and pray for their wellbeing and salvation. We ask that You reveal Yourself to them, that they may repent and turn to You. We reject any negative words spoken against us, knowing that the only words that define us are Yours. In Jesus' name, we pray. Amen."
Remember, "If possible, as much as it is up to you, be at peace with all men" (Romans 12:18, WEB). It is not our place to return curses, but to bless and pray for those who persecute us. Keep your heart focused on Jesus and His teachings.