I'm thankful for your concern for them and I'm thankful also that you realized this group was distorting what the Bible says, and that you came to a true faith in Christ.
Claiming that they, and they alone, understand what the Bible teaches is a common characteristic of many cults. To do this, they have to reject almost 2,000 years of Christian history, and they end up distorting what the Bible says or concentrating on just a few verses of the Bible and ignoring the rest. Cults often add to the Bible also, claiming their founder's writings are just as important as the Bible.
But the Bible is clear: Jesus Christ was God's only Son, sent from heaven to save us from our sins. On the cross, all our sins were placed on Him, and He took the punishment we deserve. When we commit our lives to Him and trust Him alone for our salvation, He will forgive and save us. This is why the Bible says that "Salvation is found in no one else, for there is no other name under heaven given to men by which we must be saved" (Acts 4:12).
Pray for those who are still in this group; only God can open their eyes to His truth. Then use whatever opportunities God gives you to show Christ's love to them. People may argue about your beliefs, but they can't argue about your love.