Why does it appear not level? Surely it is level, right?

Everything is in one cm increments with ikea. I’m guessing you need to take the top drawer face off and move the mounting bracket down one hole. Alternately the drawer slides need to move down one cm on side of cabinet. Do you still have all the Instructions ? You can fix this in an hour and save yourself the $50. Your contractor should be embarrassed

That contractor IMO should never enter the house again and it is just a matter of moving a rail more of a concern to me is the placement , how are you going to clean that left wall.It also looks very low.

The drawers are highly adjustable. There are small "wheels" on each rail to raise and lower the drawer front height and level the drawers. This is assuming the box is level, of course!

Something.. seems fishy here..

Drawers can be adjusted.

Is it at the right height - looks low for a floating vanity, but that could be just from the angle of the photo.

Is it next to a fixed wall or move-able components? You need enough space to get in between the cabinet and the wall to clean or you need to have a filler piece created that will seal that space against the wall.