You are assuming that the "new testament" has the authority to correctly interpret Isaiah 53. Also, Isaiah 53 cannot override the Torah.
Why do you quote the "new testament" to someone who doesn't accept it? Have you ever heard of proving something first?
Gen. 3:15, Isaiah 9:6-7; 53, Daniel 9:24-26, Zech. 12:10-14, Psalm 69; 110:1, Jer. 23 etc, etc... it’s pretty clear who This is, is it not?
Now read Matthew chapter 1 and Luke 3. The New Testament is totally Jewish, not gentile in anyway. The book of Acts is toally Jewish, and about the risen Messiah (Psalm 110:1) and His Jewish followers.
Have you tried to DISPROVE the resurrection of Jesus?
You must know (since you said you once believed in it) that the New Testament was written by the first Christ followers (called "Christians" in Antioch then all over). These people HAD seen the risen Jesus and they knew the prophecies about Him were fulfilled. If Jesus had not risen from the dead, then this movement would have died out almost immediately. There is a reason why souls are still coming to faith in Him. The God of the Old Testament (Moses and the Prophets and Psalms) still can be found when we seek Him and search for Him with all our hearts. Only by faith can we please Him.