Why does Malachi 3:7-10 say tithing but 2Corinthians 9:7 speaks of offering?

There's no contradiction in the word of God as Prov. 8:8 rightly points out that there's nothing froward or perverse in the words of God. Psalm 12:6 states that the words of the Lord are pure. The words of God are likened to silver that's purified several times in the furnace.

Both Malachi 3:7-10 and 2Cor. 9:7, as words of God have no contradictions. These tithes and offerings were commandments given to Israelites by God through Moses as Malachi 4:4 says. They're not for us but, 2Cor. 9:7 is talking to Christians and the Church.

Christians have somewhat a different version of the law. For instance, Paul wrote to Timothy in Tim. 4:4 saying every creature of God is good, even those things that were rejected by Israelites. And in Mk. 7:19, Jesus declared what Israelites thought were unclean as safe. There are laws that are no more existing in the new testament.