[Ali Imran]

God is Triune. 
Has god ever taken human form?
If he has...then you cannot say the Triune is not true.

There are eight recorded appearances in the Old Testament where God took upon Himself a physical form for a short duration. Three times He appeared as a man, once in a burning bush that was not consumed, and four times as the Angel of the Lord. Each time that this occurred it was in an extraordinary situation.

The problem is the verse where Jesus says the Father is the only true God and he is the messenger/prophet/apostle/son sent. You believe Jesus is also God which contradicts what Jesus said.

You cannot use the OT to prove God took on a human form. No Jewish scholar will agree with you.