Seatbelt Removal

Alright, it's me again with more problems.

I'm trying to remove the remnants of the seatbelts in the car. The bolt won't move at all, but there are two nuts and a plate on the underside of the car.

The bottom nut came off without a problem. There is a bigger nut though that I can't get to turn, even after spraying it with PB Blaster.

How do you all suggest I go about removing the last nut and bolt?