7 months have passed since you wrote this question so I hope that time has taken the sting out of the loss of your father. I know that this is a hard thing - to lose a loved one.
I cannot say why some Christians felt the need to tell you your father was in hell at the time of your loss. Some people lack judgment and compassion and though some of these people may have meant well, it doesn't sound like they gave you a very compassionate message.
The truth is that the Bible says that none of us are "good enough." "As it is written, There is none righteous, no, not one" (Romans 3:10), that all of us are sinners - "For all have sinned, and come short of the glory of God" (Romans 3:23) and that the wages of sin is death: "For the wages of sin is death; but the gift of God is eternal life through Jesus Christ our Lord." (Romans 6:23). We cannot earn our salvation, but can only obtain it through repentance of our sins (turning away) and accepting Jesus as our Savior and Lord of our life. "For the wages of sin is death; but the gift of God is eternal life through Jesus Christ our Lord." (Romans 6:23) We cannot earn our salvation - Our salvation is "Not of works, lest any man should boast." (Ephesians 2:9)
Jesus said, "That if thou shalt confess with thy mouth the Lord Jesus, and shalt believe in thine heart that God hath raised him from the dead, thou shalt be saved." (Romans 10:9)
"For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life." (John 3:16