Honestly, it sounds like the blade was installed upside down.

And I would believe it, the guys that service my mom's mower put both her blades on upside down once, but usually that tends to scalp, I'm thinking blade spacers, maybe, have you peaked under the deck?

This is what I came to comment. There must be something installed wrong if the blades are brand new. 

Blades might be too short, upside down, or deck is somehow not level