Canada revenue problems?

im trying to help my parents and am getting nowhere fast.my dad is 72 and is on a pension. revenue canada is garnishing his cpp which would be fine but the problem is they are taking all of his cpp which is killing my parents financially considering my mom doesnt work or collect any monies whatsoever.i have tried to get them to garnish a portion of his pension but revenue canada says there is nothing i can do.please help who can i contact because i know there is no way they can let an old man suffer like that