I completely cannot hum a song by just reading the notes?!

I completely cannot hum a song by just reading the notes?

Believe it or not , I have been learning keyboard since 2 years ago

i can get some notes, but I'm basically in the same boat. try playing it while humming, it will train your ear. or hum songs without the music that are familiar to you that you know the notes are in, that jogs your musical memory.