With patience and understanding continue to talk with him about this. Don't batter him over the head with it, so to speak, but keep trying a bit more.
I spoke to him again and he still says I don't know mommy and told me just let it go
Yeliing an dscreaming is not going to help. You've got to remain calm. Talk again with your older boy to see where he got the notion to engage in this behavior.